Bitrix24 is probably world's only free unified communications software available both in cloud and on premise.
And you get everything - enterprise social network, company instant messenger, telephony (PBX), video chat and video conferencing, email server, file sharing and project management.
If something is used for communication and collaboration, chances are it's one of the 30+ free UC tools available inside Bitrix24. API, content management and
open source code is available.
With over 30 unified communications and collaboration tools, Bitrix24 can seem a bit overwhelming at first. If you encounter any problems, please read
Bitrix24 manual in order to better
understand how each intranet component works. If you are interested in deploying Bitrix24 on your own server, require access to source code, would like to integrate Bitrix24 with other
tools you are currently using download trial version here.