Free Enterprise Grade Fax and Voip Server with full feature set.
Web based Administration of Fax Server and VoIP PBX
Fax server allows thumbnail previews, archives, uploads
VoIP Server provides full phone system with music-on-hold, scheduled conferences, web based administration, paging, parking, IVRs, and more
There is a LiveCD so you can burn an iso and test it out and an installation CD that provides an automated install of the system on a server.
There are thumbnail previews, and flash based movie tutorials available.