Development teams are using feature management as a best practice to separate code deployments from feature releases and control their feature lifecycles. LaunchDarkly is a simple offering specifically targeted at feature flagging; no free tier.launchdarkly.com
GitHub brings together the world's largest community of developers to discover, share, and build better software. Tried and true market leader for code storage.
Split provides a unified solution for feature flags, experimentation and continuous delivery, centralizing feature flag management. Split has a more complex offering than just feature flagging that includes A/B testing and experimentation. Has a free tier.