Freevo
Imagine a world where the televisie guide is liquid, where the time slots are organised to suit your schedule. imagine a place you can store all of your music, movies and photos, for you and your family to enjoy. imagine having access to all your classic games, upto the minute weather and news reports, imagine doing all of this for free. what a wonderful world that would be...stop imagining - get freevo
http://freevo.sourceforge.net/
MediaPortal
Mediaportal turns your pc in a very advanced multi-media center / htpc. it allows you to listen to your favorite music & radio, watch your video's and dvd's, use it as a digital video recorder and much more.
http://www.team-mediaportal.com/
MythTV
MythTV
http://www.mythtv.org/