Unleash – Open-Source LaunchDarkly alternative (getunleash.io)

Source code available on https://github.com/unleash/Unleash

Got SDKs for most popular programming langugages:

- Go

- Java

- Node.js

- Python

- Ruby

- .Net

- Rust

- JavaScript

- Android

- iOS

- ...and more

Don't have time to compare them now but I've been looking at flagr. This seems more polished.