My pick here would be
Bomberman Legends for the Atari Jaguar. This would have been an original entry in the Bomberman series, with support for up to
eight simultaneous players by utilizing two Team Taps (each of which could accommodate four controllers). Mike Mika (now with Digital Eclipse) and his brother Jeremy have preserved the source code.
Read more about it in
this Wikipedia article.
While we're at it, I might as well give shout-outs to a few other Jaguar games:
- Mortal Kombat 3: I think the Jaguar could have handled this game nicely. It would have been nice to see how it could have turned out.
- Return Fire: Could have been a fun romp on Jaguar CD.
- Phear: As far as I know, this is the only Jaguar game listed here that was publicly demonstrated. Although the Jaguar game was canceled, the developers ported it to Nintendo 64 and released it as Tetrisphere.
- Earthworm Jim: I've only heard about this port recently. I don't believe it got very far in development, though.