Zteam

Zteam is a mapping team, comparable to CMT. The most noticeable difference, however, is that Zteam's projects are based upon Halo 2. Like CMT, they are often accused for ripping due to the beauty of their work(they did, however, rip models and textures from Halo 2, but the tags, animations, and other content are original).

Projects
Zteam has(so far) 2 released projects on Halomaps.org - Coagulation and Sanctuary, both of which are from Halo 2.

Coagulation
Coagulation has obviously been an improvement for the all-popular Blood Gulch, although didn't quite hit the most-played multiplayer map, Lockout. This map features a script which changes how vehicles are chosen, and the weapon set is defined by gametype. For example, setting the amount of Warthogs in the map instead sets the primary light vehicle, with 1 for Ghosts, 2 for Spectres, etc.

Sanctuary
Sanctuary focuses less on vehicular combat, although there are a few light vehicles. Sanctuary is the same as Coagulation, with all it's features, but only with a different BSP, and a party music easter egg.

Imperfection
Although if you play around the map, checking things out by yourself, there are many imperfections, such the the 3rd person animations.