Lotus is an open-source pricing and billing engine that lets SaaS teams meter usage, design plans, and experiment with pricing without rebuilding their billing stack every time the model changes. You define how customers are charged: per seat, per API call, per gigabyte, in tiers, with prepaid credits, or as a bespoke enterprise arrangement negotiated over email. Plans are versioned and deployed like releases, so changing a price never means editing the plan that half your customers already signed. Usage events stream in from your product and are aggregated against each customer's plan, turning raw events into billable quantities your finance team can audit line by line. Before a new model goes live, you backtest it against historical usage to see exactly who would have paid what, and forecast the revenue before a single invoice changes. Experiments compare pricing variants on real customers, so the packaging debate ends with numbers instead of opinions. The control panel sits on top of your existing quote-to-cash stack, pulling from your payment, CRM, and data systems rather than demanding a rip-and-replace migration. Engineers integrate through the API: send events, read balances, and let Lotus handle the proration math when plans change mid-cycle. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.