what's a good feature flag tool for experiments and gradual release

A solid choice depends on whether you want simple gradual rollouts or full experimentation/A-B testing. Here are the best options I’d recommend:

Best all-around

LaunchDarkly

• Great for feature flags, gradual rollouts, kill switches, targeting
• Strong experimenting/A-B testing support
• Mature SDKs, good reliability, strong audit/governance
• Usually the default pick for teams that want a polished enterprise-grade system

Best if you want experimentation first

Statsig

• Very strong for experiments, feature flags, and metrics
• Good for incremental rollouts and product experimentation
• Often cheaper/easier than LaunchDarkly for experiment-heavy teams

Best open-source / self-hosted option

Unleash

• Good for gradual release, targeting, environment control
• Open-source and can be self-hosted
• Better for flags than deep experimentation, though you can integrate analytics yourself

Also worth considering

ConfigCat

• Simpler and often more affordable
• Good for standard flagging and gradual rollouts
• Less powerful for experimentation than LaunchDarkly/Statsig

Quick recommendation

• If you want the safest, most mature platform: LaunchDarkly
• If you want experiments + flags in one tool: Statsig
• If you want open-source/self-hosted: Unleash

If you want, I can also give you a decision table by price, ease of use, self-hosting, and experimentation depth.