Flagsmith

Flagsmith is an open source feature flagging and remote config service. It helps teams create and manage feature flags across web, mobile, and server-side applications, so features can be released behind flags and toggled without deploying new code.

Flagsmith works by wrapping code with a flag, then controlling that feature for different environments, users, or user segments. It supports segments for beta releases, A/B testing, and multivariate tests, plus organization management with orgs, projects, roles, and team members. SDKs cover 15+ languages including Typescript, .NET, and Java, with framework support including React and Next.js.

Flagsmith can be self-hosted, run on-premise or in a private cloud, or used as a hosted SaaS at app.flagsmith.com. The majority of the platform is open source under BSD-3-Clause, with a small number of repositories under MIT. Enterprise-level governance and management features require a Flagsmith Enterprise license.