While most free or open source SIP servers are Linux based (see Asterisk), it’s always nice too see solutions for other platforms as well. A few months ago I evaluated OnDO SIP Server a SIP Registrar and Proxy Server for Windows. This post will present another two, even more interesting products:
This VoIP server/client, developed by a Romanian company is continuing to receive good reviews from all over the place. Written in C++, with support for popular scripting languages such as PHP or Python, the software is portable between Linux and Windows.
3CX Phone System http://www.3cx.com/
Although not open-source, 3CX Ltd offers a free edition, supported by forums of their Windows Based PBX system.