That was not a mod I had you all playing, it was a full game called Flatout 2.
http://flatout2.sierra.com/us/IMO one of the best racing games ever made because everyone, even those that don't like to race can enjoy it. One of my friends, Humanshield, is horrible at it so he drives the tracks backwards so as to cause head on collisions.
What you experienced was the Demo derby mode. There is also a stunt mode. The only down side to this game is it is limited to 8 players at a time.
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As for mods...
2142 - starwars mod
http://www.moddb.com/mods/first-strikeI am hoping to try out a UT3 edition of carball.
http://carball.net/Some oldies from Quake 2 that I would love to find updates to:
Chaos DM
http://planetquake.gamespy.com/View.php?view=MOTW.Detail&id=79This mod simply added a whole bunch of weapons to the game including a buzzsaw, crossbow, lazer mines, broadsword, airgun....and best of all Prox Mines. The prox mines had little smiley faces (much like a alt fire flak bullet in UT) and they would hop around chasing players, laughing and giggling all the way. You could turn them on and off remotely. It was great to fill up a whole room with the little buggers (deactivated) then wait for someone to run by. As soon as someone was in the room you could turn the mines on and with an giant "WEEEEEEEEEEEEEEEEEE" in unison from the little smiley mines; there would be a most entertaining explosion.
Headhunter
http://planetquake.gamespy.com/View.php?view=MOTW.Detail&id=126The goal was to frag a player and pick up their decapitated head. Then to actually score you had to deposit the head at an altar. The more heads you carried the more points you would get at each turn in. If you were carrying a whole bunch of trophies and someone killed you all those heads would explode out from your corpse much like the rings in sonic the hedgehog and go a bouncing everywhere. This mod had a classic message when someone turned in the heads they had collected... "Soandso gave Head!"