Flagsmith is a feature flag service made by Bullet Train Ltd. A feature flag, also called a feature toggle, is a switch in the code that turns a feature on or off for some or all users without a new deployment.
Developers wrap a section of code in a flag and read the flag's state through Flagsmith's SDKs for web, mobile and server languages, or through its REST API. The dashboard sets each flag per environment, per user, for a segment of users defined by their traits, or for a percentage of users, which allows staged rollouts and canary deployments (releasing to a small group first). Each flag can also carry a remote config value, such as the color of a button, so the app changes without an app store update. Multivariate flags split users across two or more variations for A/B tests.
Flagsmith is open source under the BSD-3-Clause license. It runs as a hosted cloud service, as a private cloud instance, or self-hosted on a company's own servers. The cloud service has a free plan and monthly subscriptions priced by API requests and team members.