snom is well known in the industry for their excellent SIP based handsets. The have now released snom ONE: a robust, full-featured and secure phone system. (Windows-based edition of course!)
Mature, Robust, Secure, Windows-Based and Free
Another amazing part of this announcement is that there is a 10 extension FREE edition of snom One! (extremely reasonably priced 20 and unlimited extension versions also!) This is the real deal with no limitations--AND IT IS MATURE SOFTWARE! I've seen other products given away free that are really beta level products. But we have installed this software in the field for over a year and extensively worked with it and it is a really mature phone system.
Random Thoughts About snomONE
Below is a screen shot of the system status screen in snomONE. I love this screen because you can really get insight into the system for the last 24 hours at one glance: CPU usage, Call volume and even Call Quality score!