* [DAViCal](http://www.davical.org/) - a server for calendar sharing (CalDAV)
* [Radicale](http://radicale.org/) - A Simple Calendar and Contact Server
## Communication Systems
## Messaging
### Email
* [Cypht](http://cypht.org/index.html) - A feed reader for your email accounts - `GPL`
* [mailcow](https://github.com/andryyy/mailcow) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. `GPL`
* [Roundcube](https://roundcube.net) - A web interface to act as an IMAP frontend ([Screenshots](https://roundcube.net/screens/)) ([Source code](https://github.com/roundcube/roundcubemail/)) `GPLv3``PHP`
### XMPP
* [ejabberd](http://www.ejabberd.im) - A robust, scalable, and extensible XMPP server - `GPL``Erlang`
* [FreeSWITCH](https://freeswitch.org/) - Scalable open source cross-platform telephony platform `MPL``C`
* [HipChat](https://www.atlassian.com/software/hipchat) `⊘ Proprietary` [⛔](https://github.com/Kickball/awesome-selfhosted/pull/36) - A team chat solution with 1:1 chat audio and video, third party integration and more `PHP + Python`
* [Kaiwa](http://getkaiwa.com) A modern XMPP Web client ([Source code](https://github.com/digicoop/kaiwa))
* [Kamailio](http://www.kamailio.org/w/) - Modular SIP server (registrar/proxy/router/etc)
* [Kandan](http://getkandan.com/) – Kandan is an Open Source Alternative to HipChat. - `AGPL`
* [Kontalk](http://kontalk.org/) – Kontalk is an Open Source Messenger, similiar 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`
* [mailcow](https://github.com/andryyy/mailcow) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. `GPL`
* [Metronome](http://www.lightwitch.org/metronome) – XMPP server forked from Prosody. `Lua``MIT`
* [Mumble](http://wiki.mumble.info/wiki/Main_Page) - low-latency, high quality voice chat software `BSD``C++`
* [Node-Chat](https://github.com/IgorAntun/node-chat) - A not-so-basic open-source chat with admin features. - `MIT``Nodejs`
* [OpenFire](http://www.igniterealtime.org/projects/openfire/) - instant messaging (XMPP) and groupchat server `Java``Apache 2.0`
* [Prosody](http://prosody.im/) – Lightweight XMPP server `Lua``MIT`
* [Rocket.Chat](http://rocket.chat/) – Teamchat solution similar to Gitter.im or Slack - `MIT`
* [Roundcube](https://roundcube.net) - A web interface to act as an IMAP frontend ([Screenshots](https://roundcube.net/screens/)) ([Source code](https://github.com/roundcube/roundcubemail/)) `GPLv3``PHP`
### VoIP
* [FreeSWITCH](https://freeswitch.org/) - Scalable open source cross-platform telephony platform `MPL``C`
* [Kamailio](http://www.kamailio.org/w/) - Modular SIP server (registrar/proxy/router/etc)
* [HipChat](https://www.atlassian.com/software/hipchat) `⊘ Proprietary` [⛔](https://github.com/Kickball/awesome-selfhosted/pull/36) - A team chat solution with 1:1 chat audio and video, third party integration and more `PHP + Python`
* [Kandan](http://getkandan.com/) – Kandan is an Open Source Alternative to HipChat. - `AGPL`
* [Mumble](http://wiki.mumble.info/wiki/Main_Page) - low-latency, high quality voice/text chat software `BSD``C++`
* [Node-Chat](https://github.com/IgorAntun/node-chat) - A not-so-basic open-source chat with admin features. - `MIT``Nodejs`
* [Rocket.Chat](http://rocket.chat/) – Teamchat solution similar to Gitter.im or Slack - `MIT`
* [Tox](https://tox.im/) - A distributed, secure messenger with audio and video chat capabilities. `C``GPLv3`