Ultimate Backend

A free, MIT-licensed NestJS microservices SaaS starter with CQRS, GraphQL, and 7 core services

Best for: Teams building an enterprise-scale, multi-tenant SaaS backend who specifically want a microservices/CQRS/event-sourcing architecture rather than a monolith.
Skip if: You want a simple monolithic starter - Ultimate Backend's microservices/CQRS architecture is a significant complexity and operational overhead for smaller projects.

Ultimate Backend is an open-source, MIT-licensed multi-tenant SaaS starter kit built on NestJS with a CQRS/event-sourcing architecture, GraphQL (Apollo) and gRPC APIs, and Domain-Driven Design patterns. It ships as 7 core microservices - account, access, role, billing, notification, tenant, and project - backed by MongoDB/ArangoDB, Redis, and NATS/Event Store, with Consul for service discovery and Docker/Kubernetes deployment. It's built by Rex Isaac Raphael and has nearly 3,000 GitHub stars.

Pros

Free, open source, MIT licensed, with a large and established GitHub following (~2,900 stars)
Genuine microservices/CQRS/event-sourcing architecture is rare among SaaS starters and battle-tests DDD patterns
Comes pre-split into 7 core services (account, billing, tenant, notification, etc.) covering common SaaS domains

Cons

Microservices architecture (Consul, event stores, multiple databases) adds substantial operational complexity versus a monolith
Steeper learning curve - requires familiarity with CQRS, DDD, and distributed systems concepts
Running it locally/in production needs more infrastructure (Kubernetes, service discovery) than most solo developers need