Spreadsheets deserve an engine that anyone can embed, audit, and run on their own server. IronCalc is an open-source spreadsheet engine with a browser editor that reads and writes real Excel files: open an xlsx, edit values and formulas in the grid, format cells, and save the workbook back without a round trip through a proprietary suite. The grid feels familiar on purpose, with a formatting toolbar for fonts, fills, borders, number formats, and alignment, sheet tabs along the bottom, and templates for invoices, expense trackers, calendars, timesheets, and project plans so a new workbook starts from structure instead of a blank page. Files import from xlsx and export again to the same format, which keeps IronCalc honest as a working tool instead of a viewer. Underneath, the calculation engine is a library other software can call, so the same formulas that evaluate in your browser can also run inside a Python script, a Node service, or a WebAssembly build embedded in your own product. Self-hosting puts the whole webapp behind your own address: one Docker Compose brings up the spreadsheet server with its proxy, and teams share workbooks from infrastructure they control rather than uploading budgets to a stranger's cloud. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT and Apache-2.0 dual licensed.