OK, here's one - and I'll be amazed if someone gets it. But this is NeoGAF, and I should know better than to underestimate the community here.
Almost a decade ago, I signed up for the super computer club at school where we built computers that ran linux. When we finished, each computer had a multiplayer capture the flag tank game installed. It was 3D, but certainly not a looker. We played the shit out of it though. I remember going home to play Mercenaries on PS2 at the time. It had just released, if that helps?
Anybody know what the heck that was? Man, I'd love to find a way to play it again today...