* [Kontalk](http://kontalk.org/) - Kontalk is an Open Source Messenger, similar to WhatsApp (app for android only currently), including end-to-end encryption, server is based on Tigase XMPP Server. ([Source Code](https://github.com/kontalk)) `GPLv3``Java`
* [Metronome IM](https://metronome.im/) - Fork of Prosody IM. ([Source Code](http://code.lightwitch.org/)) `MIT``Lua`
* [Metronome IM](https://metronome.im/) - Fork of Prosody IM. ([Source Code](https://github.com/maranda/metronome/)) `MIT``Lua`
* [MongooseIM](https://www.erlang-solutions.com/products/mongooseim.html) - Mobile messaging platform with a focus on performance and scalability. ([Source Code](https://github.com/esl/MongooseIM)) `GPLv2``Erlang`
* [Openfire](http://www.igniterealtime.org/projects/openfire/) - Real time collaboration (RTC) server. ([Source Code](https://github.com/igniterealtime/Openfire)) `Apache``Java`
* [Prosody IM](http://prosody.im/) - Feature-rich and easy to configure XMPP server. ([Source Code](http://hg.prosody.im/)) `MIT``Lua`