Unleash Feature Flags

Unleash is an open-source feature management platform that provides feature flags, toggles, and progressive delivery capabilities for engineering teams. Originally created by Ivar Conradi Osthus and the team at Finn.no (Norway's largest classifieds site) in 2014, Unleash was spun out as an independent company in 2019 and has over 12,000 stars as of 2026. Unleash is designed to be privacy-first and self-hosted, giving teams full control over their data while providing enterprise-grade feature flag management. Key features include: feature toggles (gradually rolling out features to subsets of users based on strategies like percentage rollout, user ID lists, IP ranges, and custom constraints), strategies (built-in strategies including default, gradualRollout, userWithId, remoteAddress, flexibleRollout, applicationHostname, and custom strategy plugins for complex targeting logic), variants (A/B testing with configurable variants for feature experiments, supporting weighted distribution and payload customization), constraints (fine-grained targeting using context fields like environment, region, user segment, and custom attributes), activation strategies (combining multiple strategies with AND/OR logic for sophisticated rollout control), metrics and analytics (tracking feature usage, impression counts, and experiment results with built-in dashboards), change management (audit logs, change requests, and scheduled changes for controlled feature releases), project and environment organization (managing features across projects with environments like development, staging, and production), SDK support (client-side and server-side SDKs for 24 languages including JavaScript, Python, Java, Go, Rust, Ruby, .NET, PHP, Swift, Kotlin, and Flutter), edge deployment (running Unleash at the edge for sub-millisecond flag evaluation), and self-hosted or managed cloud deployment.