Bullet Train
Open SourceOpen-source Rails SaaS framework — teams, invitations, roles, a themeable Tailwind UI, REST API with outgoing webhooks, and a 'super scaffolding' generator that builds CRUD for your domain models. MIT core, paid pro modules.
Why we recommend Bullet Train
Bullet Train is the open-source counterweight to paid Rails SaaS templates: the MIT-licensed core gives you user accounts, teams, invitations, roles, and a REST API with outgoing webhooks — the entire undifferentiated middle of every B2B app — for free. Its signature idea is 'super scaffolding': you describe a domain model and it generates the full stack for it (model, strong params, views, API endpoints, tests) following the framework's conventions, which keeps a growing codebase eerily consistent. Andrew Culver built it from years of consulting on Rails SaaS, and it reads like distilled experience rather than a demo. Revenue comes from optional paid modules and support, so the core's incentives stay aligned with users.
Best use cases
Best for: Rails teams that want a free, auditable foundation with real multi-tenancy, developers who like code generators that follow them through the project instead of only day one, and companies that need to own every line for compliance reasons.
Honest limitations
Not for: developers who dislike heavy conventions — super scaffolding produces a lot of framework-flavored code you must learn to read. Billing is not in the free core (bring the Pay gem or a paid module). Smaller community than stock Rails idioms, so some answers only exist in its docs and Discord.
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