Flagsmith

Flagsmith is a feature flag and remote configuration platform that lets you toggle features, run A/B tests, and manage settings without redeploying. It's a remote control panel for your application's behavior. BSD 3-Clause, Python backend. Supports feature flags, remote config (change values without deploying), A/B testing, and user segmentation. SDKs for every major language: JavaScript, Python, Java.NET, Go, Ruby, iOS, Android. The admin UI is clean and non-developers can toggle flags without touching code.

Self-hosting is free. Docker Compose setup, Postgres backend, works with your existing infrastructure. Every feature is available in the self-hosted version, no feature gating. Flagsmith Cloud free tier: up to 50,000 requests/mo. Startup plan at $45/mo for 1M requests. Scale plan at $500+ for higher volume with SLAs and audit logs.

Solo devs: self-host or use the free cloud tier, both work. Small teams: free cloud tier handles most early-stage apps. Medium teams (10-50): self-host to avoid per-request billing, or pay $45/mo if ops time isn't worth it. Large: self-host or negotiate enterprise pricing.

The catch: the self-hosted version needs Postgres and can require Redis for caching at scale. If you just need simple on/off flags, environment variables or a config file might be enough. Flagsmith shines when you need segmentation, gradual rollouts, and A/B testing.