Descent
Levels by Tom
Zora is named for my mother.
The level has 2 plasma cannons, 3 sets of quads, 2 fusions, 1 vulcan, 1 smart, and 2 homers.
It's fairly interconnected and plays fairly fast.
Here are a few screenshots:
Tetrafusion (aka monkey tent) is a level for D1 based on a geometric shape called a Tetrahedron.
The level has 4 fusion cannons, no missiles, and no reactor.
The level has no definite "up" or "down" directions, so keep your wits about you!
It makes for some excellent one-on-one action, and is pretty good with 4 players.
Here are a few screenshots:
Animated gif of a match in Tetrafusion (191K)

Octave (aka monkey house) is a level for D1 shaped like an Octahedron.
The level has 6 plasma cannons, no missiles, and no reactor.
The level has no definite "up" or "down" directions.
Notice the players are oriented differently in many of the screenshots!
It's a fast and furious level for one on one, and will make your head hurt after too long.
Here are a few screenshots:
Monkey Bars is a level for D1 shaped like a big cube.
The level has 2 full sets of primaries, 2 smart missiles, and no reactor.
The level has no definite "up" or "down" directions, which forces some interesting combat.
It was the inspiration for the other levels on this page.
Here are a few screenshots: