Surprised this hasn't been posted, it's pretty old news, but free is free. They are offering it free to "celebrate the upcoming release of Tribes: Vengeance". Tribes 2 was free too, at FilePlanet, but they ran out of keys or something.
FilePlanet (I hate them but you might not) -
http://www.fileplanet.com/promotions/tribes/
3D Gamers -
http://www.3dgamers.com/games/tribes/
Gamers Hell -
http://www.gamershell.com/download_6159.shtml
FilePlanet (I hate them but you might not) -
http://www.fileplanet.com/promotions/tribes/
3D Gamers -
http://www.3dgamers.com/games/tribes/
Gamers Hell -
http://www.gamershell.com/download_6159.shtml