The Ultiverse group thread has a pretty high degree of momentum going on.
PM the group thread leader, ch0sen1, for details.
In brief, its an original universe and you can be whatever or whomever you wish. The thread has just reached 8 pages and still going strong. We've already had at least one major battle that leveled a part of Boston, MA and are building into a major story arc once this current thread completes. The current thread is an "Origins" storyline, so its easiest for everyone to drop in and get their feet wet.
For some reason, the vast majority of heroes are magic-based, but this is not a prerequsite by any means.