Best of Open Source Professional Programs

This website offers a list of the best open-source (for our purposes "open-source" = "FREE") programs for

productivity

networking

collaboration

...and more.

http://www.infoworld.com/ifwclassic/weblog//tcdaily/archives/2007/10/preview_openpro.html

Scroll down to read the written articles.

Pardon the broken image thumbnails and the cache layout. The list at the top of the page is a useful compilation of award-winning open-source programs.