Feature Flags

3 open source tools compared. Sorted by stars — scroll down for our analysis.

Tool	Stars	Velocity	Language	License	Score
Unleash Open-source feature management platform	13.3k	+28/wk	TypeScript	Apache License 2.0	77
GrowthBook Open source feature flags and experimentation	7.4k	+19/wk	TypeScript	—	63
Flagsmith Open source feature flagging and remote config	6.3k	+9/wk	Python	BSD 3-Clause "New" or "Revised" License	73

Our Analysis

Unleash13.3k★

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.

GrowthBook7.4k★

GrowthBook is feature flags plus experimentation for teams who think LaunchDarkly's pricing is absurd — and they're right. Open-source (MIT), self-hostable, with a Bayesian statistics engine that connects directly to your data warehouse for A/B test analysis. No per-seat fees, no per-flag limits. Your infrastructure, your data, your cost. If you're an indie hacker who wants feature flags and A/B testing without a $500/month bill, GrowthBook is the obvious choice. LaunchDarkly is the enterprise standard with better safety automation and compliance workflows. Unleash is the open-source alternative focused purely on feature management. Statsig is the managed option with more advanced analytics. The catch: GrowthBook's flag management is less mature than LaunchDarkly's — flag dependencies, complex scheduling, and approval workflows are still developing. The experimentation features assume you have a data warehouse (BigQuery, Snowflake, etc.) for results analysis. And self-hosting means you're responsible for uptime of a tool that controls feature rollouts — if GrowthBook goes down, your flags freeze.

Flagsmith6.3k★

Flagsmith gives you feature flags with something Unleash doesn't: identity management built in. It stores user traits server-side, so your flags can target specific users without your app shipping context on every request. For microservice architectures, that's a meaningful architectural win. Unleash is the bigger OSS player — more GitHub stars, larger community, and a free tier for small teams. LaunchDarkly is the commercial heavyweight at enterprise pricing. GrowthBook blends flags with experimentation if you need A/B testing too. Use Flagsmith if you need remote config alongside flags and want one tool for both. The BSD license is business-friendly, and self-hosting is straightforward. The catch: smaller community than Unleash (6K vs 13K stars), which means fewer tutorials and community-built integrations. Paid plans start at $99/month — pricier than Unleash's $49 entry. If you're a solo dev who just needs basic on/off flags, Unleash's free tier is more generous.