LastSaaS is a complete SaaS platform you can fork and start building on. Go 1.25 backend, React 19 + TypeScript frontend, MongoDB, Tailwind CSS 4. MIT licensed.
What you get on day one:
OAuth (Google/GitHub/Microsoft), magic links, MFA, JWT with refresh rotation
Stripe subscriptions, per-seat pricing, credit-based billing, invoices, tax handling
Multi-tenant architecture with 3-tier RBAC, tenant isolation, team invites
White-labeling: custom domains, themes, CSS, configurable landing pages
19 webhook event types with HMAC-SHA256 signing, delivery tracking, retries
Admin dashboard with health monitoring (8 charts), user impersonation
MCP server with 26 tools for AI-assisted app management
The entire codebase was written through Claude Code — not as a novelty, but to produce code specifically structured for AI agents to navigate and extend. Fork it, point your coding agent at it, build your product logic on top.
It's running in production powering Flipbook (a presentation hosting platform I built on it). Deploys as a 14MB Docker image on Fly.io for ~$5/month.
Full writeup on the architecture: https://meditations.metavert.io/p/the-last-saas-boilerplate
Happy to answer questions about the Go architecture, the multi-tenancy model, or the experience of building this through agentic engineering.