Do you mean you want recommendations for open‑source feature‑flag/feature‑toggle platforms you can self‑host or integrate into apps? Below are the most mature options, with a short summary of strengths, languages/SDKs, and when to pick each.
Top open‑source feature‑flag tools
- Unleash
- Language/stack: Server in Java/Node/Go (official), wide SDK support (JS, Java, .NET, Go, Python, Ruby, PHP, mobile).
- License: MIT
- Key features: Flexible strategies, segments, constraints, gradual rollouts, A/B test support, proxy for low latency, audit logs, UI.
- Good for: Production‑grade self‑hosted setups with multi‑language apps; strong community and extensibility.
- Repo: unleashorg/unleash
- Flagsmith
- Language/stack: Python/Django backend; SDKs for many languages.
- License: MIT
- Key features: Feature flags + remote config, traits/identities, environments/projects, API + dashboard, hosted SaaS available.
- Good for: Teams that want a simple dashboard and remote config alongside flags; easy to self‑host or use hosted plan.
- Repo: Flagsmith/flagsmith
- Flagr
- Language/stack: Go backend, UI, SDKs.
- License: Apache 2.0
- Key features: Evaluation API, experiments, variant allocations, REST API, SDK integrations.
- Good for: Lightweight Go‑based service focused on experimentation and rollout logic.
- Repo: checkr/flagr
- FeatureProbe
- Language/stack: Java backend, SDKs for many languages (popular in Asia).
- License: Apache 2.0
- Key features: Strategy rules, percentage rollout, environments, UI.
- Good for: Simpler self‑hosted option if you want a Java ecosystem project.
- Repo: FeatureProbe/FeatureProbe
- Flipper (library)
- Language/stack: Ruby (gem) — primarily a library rather than a centralized server.
- License: MIT
- Key features: Toggle strategies, adapters (Redis, ActiveRecord), simple UI via plugins.
- Good for: Ruby/Rails apps that can manage toggles in‑process or via shared storage.
- OpenFeature (spec / SDK abstraction)
- Not a flag backend — it’s a vendor‑neutral SDK spec that standardizes how your app reads flags. Use with a backend provider (Unleash/Flagsmith/etc.) via a provider implementation.
- Good for: Teams wanting multi‑provider flexibility and consistent SDK usage across languages.
- Repo: openfeature
Other notes
- Commercial/self‑hosted choices: Some projects (Flagsmith, Unleash) also offer hosted/cloud options if you don’t want to manage infra.
- Hosted commercial leaders (not open‑source): LaunchDarkly, Split — consider if you need enterprise features and managed service.
- Integration considerations: SDK availability for your languages/platforms, latency (server vs SDK polling vs proxies), persistence/audit needs, RBAC, metrics/experimentation, and ease of operation (DB, clustering).
Quick pick recommendation
- If you want a robust, widely adopted OSS system: try Unleash.
- If you want remote config + flags and an easy self‑hosted path: try Flagsmith.
- If you want a lightweight Go solution focused on experiments: try Flagr.
- If you use Ruby primarily and prefer an in‑process toggle library: use Flipper.
If you tell me your stack (languages, cloud/on‑prem, need for experimentation vs simple flags, scale, and whether you want hosted), I can recommend one and outline deployment/SDK integration steps.