I am wondering if anyone has any suggestions for software that would allow for group designing. I know some people use wiki's I was thinking something like Google docs with links to pages inside the overall document or to have links to other Google doc pages. This is for a sandbox multiplayer mmo kit so it would be more technical and less about following story arcs etc.

This is one of the things that I thought Google Wave could be used for. Alas, Google has discontinued all work on that.

There is the continuation of that project- http://incubator.apache.org/wave/index.html - Apache Wave - which is still in its infancy, but if you're interested, it's something to keep an eye on, or mess around with for collaboration. Until it becomes fully functional though, the options Tom listed above are more or less the most useful.

Trello.