Unleash

The most battle-tested open source feature flag platform, period. Founded in 2015 by Norway's largest marketplace, Unleash has had nearly a decade to mature while competitors scrambled to exist. If you're running a SaaS and want gradual rollouts without handing LaunchDarkly $10K+/year, this is your move. GrowthBook is the main OSS rival — lighter, more experiment-focused — while Flipt is simpler but less feature-rich. Flagsmith rounds out the field with a generous free cloud tier.

You get targeting, A/B testing, and SDKs for everything. Self-host it and your user data never leaves your infrastructure — a real selling point post-GDPR. The community edition handles most indie needs.

The catch: RBAC, audit logs, and approval workflows are Enterprise-only. The OSS version has no governance features, so if you're a team of five shipping to production, you're flying without guardrails unless you pay up. Also, no multi-context targeting — it's single-context constraints only.