I have had a few people ask me questions on some open-source or alternative portal sites to sharepoint. I have seen a few linux based systems that perform similar tasks to sharepoint but nothing that was on the windows side. Until recently, I ran across (http://www.alfresco.org/)
Alfresco is a great project that allows for a good alternative. I was able to install in a few min (about 20) on windows. They also make a linux version. So go look at the site and view the flash demo.