Growth Book is an open source experimentation platform designed for companies that want to bring A/B testing in-house, but don't want to build it themselves.

Izanami is a shared configuration, feature flipping and A/B testing service perfectly well suited for micro services environment written in scala and developed by the MAIF OSS team.
Izanami provides a friendly UI for non-tech users as an HTTP REST API you can call using you favorite language.

Izanami also provides first class integration. Java, Scala, Node and React and CLI clients are available to integrate Izanami with your application.

Perti is Wix’s holistic experiment system, it covers the lifecycle of product experimenting including A/B tests and feature toggles.

Flagr is an open source Go service that delivers the right experience to the right entity and monitors the impact. It provides feature flags, experimentation (A/B testing), and dynamic configuration. It has clear swagger REST APIs for flags management and flag evaluation.

Sixpack is a language-agnostic ab testing framework
Sixpack makes it easy to run A/B tests across multiple web services written in different languages.
It includes a beautiful dashboard for viewing test results and choosing winners.