The ABH 2.5 engine (Which is just the name while being developed) will be a fairly advanced game with custom weapons (You can have about 80 custom weapons at once) all with custom images, sounds, properties etc. which are easily set from an external file.
It will also have a level editor which is also currently being worked on, and it will support semi-transparencies, custom images with any size, etc.
The multiplayer engine haven't been much started on, (Except that I'm learning by making a simple visual chat game where people walk around and have chat bubbles over their head, so that I can learn MooClick properly).
We only have 1 music composer, 1-2 artists and 1-2 programmers working on it, and would happily accept volunteers.