GrowthBook

GrowthBook is an open-source feature flag and A/B testing platform that runs entirely in the browser or serverless environments. It combines feature management with statistical analysis for experiments directly within the codebase. The tool supports complex targeting logic, including user properties and geo-location rules. Developers appreciate its lightweight nature and ability to function without a heavy backend.

This solution is ideal for frontend-heavy teams who need tight integration with analytics tools like Segment or PostHog.