Teams that cannot send messages through someone else's cloud run Mattermost - the open-core, self-hosted alternative to Slack. It provides public and private channels, threaded discussions, unlimited search history, file sharing with previews, one-to-one audio calls, and screen sharing, with desktop clients for Windows, macOS, and Linux plus iOS and Android apps. Messages support full Markdown, which suits engineering conversations with code blocks and logs. Playbooks turn repeatable processes such as incident response and release management into checklist-driven workflows with automated triggers and retrospectives. Integration is a core strength: prebuilt connectors for GitHub, GitLab, Jira, ServiceNow, and PagerDuty, plus webhooks, slash commands, bots, a REST API, and a plugin marketplace with 700+ entries - together making it a working surface for ChatOps rather than just a chat room. Playbooks add keyword and event triggers, task assignment, status broadcasting, and post-incident retrospectives, so operational knowledge is not trapped in individuals' heads. The server is a single Go binary backed by PostgreSQL, with React clients, released monthly under MIT license and deployable fully air-gapped - which is why governments and defense organizations run it inside closed networks, and why the same control applies to any team with confidentiality requirements. The compiled Team Edition is free for unlimited users with no message history cutoff, so costs stay flat as the team grows.

Blast off into productivity space with Rocket.Chat SIX, the ultimate team collaboration cosmos! Imagine a place where your messages, tasks, and projects all live in harmony, orbiting around your team's efficiency like a well-organized galaxy. This isn't just any old chat platform; it's a customizable universe where you're the master of your data domain, with the power to tweak, integrate, and innovate to your heart's content. Ready to provide stellar customer service? Engage with your clients in a way that's so contextually on-point, they'll feel like you're mind-reading across the cosmos. Plus, with a chat engine that's like a gravitational pull for user engagement, your app or website will become the center of your users' universe. And for the security-conscious space cadets, fear not! Rocket.Chat SIX is locked down tighter than a spaceship hatch, with end-to-end encryption and a buffet of deployment options to satisfy your security appetite. All this, hosted on RepoCloud, where the cost is as lightweight as zero-gravity. So why settle for a terrestrial tool when you can have a celestial experience? Rocket.Chat SIX: because your team deserves to collaborate in a universe that's light-years ahead!

Matrix's flagship client, built by the protocol's creators: Element brings the decentralized open standard for real-time communication to web, desktop, iOS, and Android. Paired with a Matrix homeserver, it delivers Slack-quality team messaging where you own every message, file, encryption key, and byte of metadata. End-to-end encryption is on by default, built on Olm and Megolm - the Double Ratchet algorithm family Signal popularized, extended for large-room scalability and publicly audited by NCC Group. Messages encrypt per-device with cross-signed device verification, so even a compromised server yields nothing readable. Federation is the defining capability: like email, users on different homeservers converse seamlessly, and 30+ bridges connect Matrix rooms to Slack, Discord, WhatsApp, and Telegram, so moving to sovereign infrastructure doesn't sever contact with anyone. Rooms support threads, reactions, file sharing, and voice and video calls via Element Call. The result is digital sovereignty chosen by governments and enterprises across Europe: your data sits on your server in your jurisdiction, portable to any other Matrix host because the protocol is an open standard. Apache-2.0 licensed, with no per-user fees at any scale.

Used by the Rust language community, NASA, Dropbox, and thousands of organizations worldwide with over 25,600 GitHub stars and 1,500+ contributors, Zulip is the only modern team chat app designed from the ground up for both real-time and asynchronous communication through its unique topic-based threading model where every message belongs to a named topic within a channel. This eliminates the context collapse of linear chat by letting teams follow specific conversations without scrolling through unrelated messages, resume threads days later without losing context, and catch up on missed discussions at per-topic granularity. Server 12.0 introduced end-to-end encryption for mobile push notifications, AI-powered search ranking, channel folders for workspace organization, and expanded video conferencing with Jitsi, BigBlueButton, and Zoom integration. Over 100 native integrations connect GitHub, GitLab, Jira, Sentry, PagerDuty, Travis CI, Redmine, dbt, Nextcloud, and n8n with bidirectional notifications, while LLM-driven agents access web-public channels via a standard llms.txt interface. Full-text search covers unlimited message history across all plans, code blocks render with syntax highlighting for 250+ languages, and LaTeX math expressions display inline. The REST API with typed Python and JavaScript SDKs enables custom bots, webhook integrations, and programmatic administration. Import tools migrate entire workspaces from Slack, Microsoft Teams, Mattermost, and Rocket.Chat. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

Your team chat can be one executable on your own server: Campfire Rust runs rooms, direct messages, attachments, and search as a single binary that replaces the whole Ruby, Puma, Redis, Resque, and Thruster stack. Create rooms with access controls for projects, departments, or a private board discussion, and keep direct messages beside them for quick questions. File attachments arrive with previews, mentions pull the right person into a thread, and search finds the decision someone made months ago. Web Push notifications reach browsers and phones, so a quiet room still finds its people when it matters. Chatbots connect through a simple HTTP API for sending and receiving messages and attachments, which makes Campfire a home for build alerts, deploy notices, and support pings. Existing Campfire installs upgrade in place because the Rust binary reads the same SQLite database, storage layout, and signed cookies, with no data migration and no mass sign-out. Automatic TLS with Let's Encrypt certificates, HTTP/2, and Action Cable-compatible WebSockets are built in, and the whole system works on air-gapped networks that never touch the internet. Run it as your primary chat, as a backup for the day a hosted service goes down, or as a walled garden for executives and events. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Stoat delivers a complete Discord-like community chat experience that organizations can self-host on their own infrastructure with full data ownership. The platform provides text channels organized in categories, real-time voice calls powered by LiveKit, file sharing with automatic media proxying, custom emoji support, bot framework, GIF search, server invites, and granular role-based permissions — all wrapped in a polished web UI that feels immediately familiar to Discord users. The architecture separates concerns across dedicated Rust binaries handling the REST API, WebSocket real-time events, file storage with S3-compatible backends, push notifications, and media proxying, backed by MongoDB for persistence and Redis for caching. Web, desktop, and mobile clients connect through the same API, ensuring consistent experience across platforms. Unlike federated alternatives such as Matrix, Stoat provides a single-server deployment model focused on the Discord-style community experience: server invites, channel categories, member management, and an invite-first onboarding flow that communities expect. The Docker Compose deployment stack handles all microservices with Caddy providing automatic TLS via Let's Encrypt. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Think of it as a team messaging platform where every feature beyond core chat is a plugin you can install or remove, inspired by VS Code's extension model but applied to real-time communication. The Moleculer microservice backend scales horizontally across nodes while Socket.io delivers instant message synchronization with text, images, files, mentions, reactions, and rich Markdown formatting. Available plugins provide LiveKit video conferencing, collaborative drawing boards, task management panels, end-to-end encryption, custom themes, and third-party push notification reception without touching core code. Groups use a two-level space system with customizable panel layouts arranged through drag-and-drop, while role-based access control enforces fine-grained permissions across the organization. The Open Platform exposes OAuth for single sign-on across connected applications and a Bot API enabling bidirectional message processing between Tailchat and external services via HTTP requests. Multi-platform clients cover web, Electron desktop with screenshot capabilities, and mobile apps with native push. Docker Compose deployment bundles MongoDB for persistence, Redis for caching and transport, and MinIO for S3-compatible file storage. Deploy on RepoCloud with a dedicated VPS for persistent team infrastructure under the Apache 2.0 license.

Fluxer gives friends, gaming groups, and private communities their own self-hosted instant messaging and VoIP platform that replaces Discord with private text channels, voice rooms, video calls, and screen sharing. Members can chat one-on-one in direct messages, form multi-person group conversations, or organize large community servers into categorized text and voice channels with threaded replies, reactions, and typing indicators. When a conversation moves to voice, participants can join low-latency audio and video rooms from multiple devices simultaneously, share application windows or full screens, and rely on built-in noise suppression and echo cancellation for clear calls. Rich media support allows users to share file attachments, preview embedded links, search animated GIFs through KLIPY, and upload custom community emojis and stickers. Server administrators control access through role-based permission hierarchies, member timeouts, kicks, bans, and detailed moderation audit logs that track every configuration change across the community. Integrated full-text search lets members quickly locate historical messages, code snippets, and shared files across every channel they can access. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Discord, except the server in the sidebar is a server you actually own. Backspace gives a community its spaces, categorized text channels, group direct messages, and friend lists, then adds calling that treats quality as a setting rather than a subscription tier. Share a screen at up to 4K and 120 frames per second, choose the codec and bitrate yourself, give every participant and every stream its own volume slider from silent to double, and watch a live inspector report each connection's ping, jitter, and packet loss while noise suppression keeps the mechanical keyboard out of the call. Servers stop being islands, too: peer your instance with a friend's and friendships, direct messages, calls, and presence cross between them while each owner keeps their own rules, bans, and audit trail. Find people across the federation, decorate a profile, set a custom status, and search old messages by sender, date, or attachment. Admins shape it all from one panel, from registration gates and storage down to a per-resolution bitrate matrix for streams. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Openfire is a self-hosted XMPP server that gives your organization its own instant messaging network, with one-to-one chat, persistent group rooms, and federation to other XMPP servers, all administered from a web console. Team members connect with any XMPP client on desktop, mobile, or the web and get presence, rosters, offline message delivery, and file sharing inside conversations. Multi-user chat rooms stay available around the clock with configurable history, moderation roles, and access controls, so a support channel or project room keeps its context instead of dissolving into scattered direct messages. The plugin catalog installs from inside the admin console and adds capabilities like message archiving and compliance monitoring, a browser-based chat client, HTTP file upload, and push notifications for mobile clients. An LDAP directory or an existing database can supply users and groups, so accounts stay in sync with the directory your organization already maintains. Server-to-server federation connects your users with contacts on other XMPP domains over encrypted connections, and load balancing spreads busy deployments across multiple instances. TLS certificates, encrypted client ports, and IP-based access lists for the admin console keep the deployment under your control from the first setup wizard onward. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

Your chat server should be able to talk to everyone else's chat server: Synapse is the reference homeserver for the Matrix network, hosting your users, rooms, and message history on infrastructure you control while federating openly with thousands of other servers. People keep their own identity on your domain and still message friends, colleagues, and communities elsewhere, because rooms are shared across servers instead of locked inside one company's silo. Any Matrix client works against it, from Element on phones and desktops to a shelf of community clients, and end-to-end encrypted conversations stay readable only by their participants. Bridges and application services wire the network into Slack, Discord, Telegram, IRC, and other systems, so existing conversations can move across gradually instead of in one painful migration weekend. Single sign-on through SAML or OpenID Connect folds chat accounts into the identity provider your organization already runs, and guests, registration controls, and rate limits stay in your hands. Media uploads, message history, and user data live in your PostgreSQL database and your file storage, with retention and federation policies set per room or for the whole server. When one process is no longer enough, worker processes split the load, Prometheus metrics show where it goes, and the admin API handles accounts, rooms, and moderation programmatically. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Running chat for a dozen people is easy; running it for a city-sized crowd, on servers you control, with group rooms, archived history, and phones that still buzz when the app is closed, is the job MongooseIM was built for. MongooseIM is an XMPP server at the core of a messaging platform, so any standard XMPP client on desktop, mobile, or web can connect, and browser clients reach it over WebSockets or BOSH. Group conversations run in multi-user chat rooms, message archive management keeps searchable history on the server, and message carbons deliver real-time copies to every signed-in device a person owns. Offline messages wait for reconnecting clients, rosters carry contact lists and presence, and privacy settings plus vCard profiles round out the everyday chat features. Operators manage users, rosters, messages, and settings through a GraphQL API over HTTP or the mongooseimctl command line, and more than fifty built-in metrics show what is happening inside each node. Accounts authenticate against internal storage, MySQL, PostgreSQL, Cassandra, LDAP, or external scripts, and multi-tenancy support creates thousands of chat domains dynamically on one deployment. Adding cluster nodes raises capacity as the audience grows, and the companion push component wakes mobile apps through push notifications. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-2.0 licensed.

Why rent your messaging from a corporate walled garden when Tinode runs WhatsApp-style chats, groups, channels, and calls on a server you control? Teams get one-on-one and group chats that stay in sync across web, Android, and iOS, with typing indicators, delivery and read receipts, presence, replies, forwarding, editing, pinned messages, and notes to self. Communities broadcast through read-only channels with an unlimited number of subscribers, and granular permissions decide who can read, write, or invite on each topic. Support desks welcome anonymous visitors, mark staff and verified accounts with badges, and put chatbots to work with forms and templated replies. Messages take markdown-style formatting, inline images and videos, file attachments, and voice messages. One-to-one voice and video calls run peer to peer over WebRTC, using the TURN and STUN servers you configure. Administrators block unwanted contacts on the server, attach moderation plugins over gRPC, and script the rest with a command-line tool. Attachments can sit on local disk or Amazon S3, the database can be MySQL, PostgreSQL, or MongoDB, and sharded clustering with failover scales past one server. The clients offer light, dark, and system themes, custom chat wallpapers, and translations for more than a dozen languages. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Most team chat keeps people in one app and AI agents in another; Octo Server is the backend that puts both in the same conversation. It powers the OCTO workplace, where Lobsters, the platform's OpenClaw-powered AI agents, sit in channels as first-class participants that read context, run tool calls, and report back alongside their human teammates. Every request flows through one pipeline: token and cookie authentication, organisation-aware role checks and per-channel permissions, business logic that can start or resume an agent session, then fan-out through WuKongIM for real-time delivery. Channels support threaded subspaces, shared files, and a GROUP.md document that stores the group's standing context where the whole team can edit it. The smart summary service reads busy channels and produces structured digests, so catching up means reading one brief instead of hundreds of messages. External bridges connect conversations to GitHub, WeCom, Feishu, and Loop through adapters, and webhooks push group events to your own systems. The official one-command deployment runs the server with the web client, admin console, task service, WuKongIM, MySQL, Redis, and MinIO behind nginx, scaling as one backend that every client speaks to. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

With nearly 5,000 GitHub stars and a Hacker News launch that garnered 147 points, Colanode delivers the first genuinely local-first alternative to both Slack and Notion in a single self-hosted workspace — writing every operation to a client-side SQLite database before syncing to your server, so teams work at full speed offline, on planes, or through intermittent connections without ever losing a draft. The real-time chat system provides channels and direct messages with instant delivery via WebSocket, while the rich text editor offers Notion-style block-based pages for documents, wikis, meeting notes, and knowledge bases with headings, code blocks, embeds, and nested hierarchies. Customizable databases organize structured data with custom fields and three dynamic views — table for spreadsheet-style browsing, kanban for visual workflow boards, and calendar for time-based planning. Conflict-free Replicated Data Types powered by Yjs handle concurrent editing across pages and database records: multiple users modify the same document simultaneously and the system merges changes automatically without manual conflict resolution. File management supports upload, sharing, and organization within workspaces using pluggable storage backends including local filesystem, S3-compatible services, Google Cloud Storage, and Azure Blob Storage with TUS resumable uploads for large files. The server runs Fastify with Zod validation on Node.js 20+, persists to PostgreSQL with pgvector extension, uses Redis for event broadcasting, and deploys via a single Docker image. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

Orbit puts your team's tasks, documents, and conversations in one workspace on your own server, so planning work no longer means checking three separate apps. Task projects carry your own workflow: switch between list, board, and timeline layouts, drag work between statuses, break large efforts into sub-issues, and link related tasks with an activity feed recording every change. Saved views keep preferred filters one click away, and personal pages like My tasks, This week, and Overdue show what needs attention today. Documents live in a page tree with teamspaces and favorites; the rich editor supports tables, code blocks, and checklists, several people can write at once with visible cursors, version history keeps earlier drafts recoverable, and a Notion importer brings existing pages across. Chat sits beside the work rather than in a separate silo: channels, direct messages, threads, files, reactions, and search, with links to tasks and pages unfolding into previews inside the conversation. GitHub sync turns labeled issues and pull requests into tasks and completes them when pull requests merge. AI clients connect through a built-in MCP server with OAuth, so an assistant can read your projects with the full context of your workspace while the data never leaves your server. Administrators manage workspaces, members, roles, API tokens, audit logs, and scheduled backups to S3 from the same interface. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.