The basic rundown for the AU as it stands is:
There is no Brotherhood, not as it's known in canon. Of course there are bound to be mutants unhappy with the way humans tend to treat them, with how they're considered dangerous (and with the budding legislative efforts to keep an eye on them), but they haven't yet formed anything but small, localized groups. What resistance exists is disjointed, disorganized, and scattered-- and it's slowly gaining momentum, if not gaining any ground. There isn't a solid opposition yet; the number of individual groups, though, has been on the rise since the mutant issue became a permanent part of nightly news reports.
One such group is starting to find its footing inside Xavier's, fueled by its members' discontent. Individual reasons vary just as much as they themselves do-- belief in their superiority, a desire to take more action, or hell, even boredom-- but they all have one thing in common. They believe that there's a better way to do things, and it's not going to happen if they stick with the school's MO.
For individual characters:
If you're playing a canon character: you're welcome to keep them pretty close to that so long as you keep in mind that the movies basically didn't happen. Go ahead and AU events in if you really want particular bits of development to be there, just make sure it still fits with the fact that there hasn't yet been any large-scale resistance and legislative efforts are just starting. Local protests are about as big as it gets at this stage. Teachers can stay teachers, or you can AU them into a younger version and play them as a student (and vice versa, if you want to AU a student as an adult instructor.) Non-canon characters basically have the same guidelines; all that's asked is that your AU version fits into the setting.
The Taken page hasn't been fancied up yet, but just as an fyi ahead of time, it'll be asking for the following information: player, character name, their original series, their AU status (student/instructor, age, and possibly their affiliation, though since that's very open to change over the course of play I doubt I'm putting it in there) with at least a brief description of the AU version, and their power, also with a short little description just so we all know what they're working with. Not asking for much here, just something like 'can lift and move objects up to about X size/weight' for a telekinetic.
There is no application page, all you're going to need to do is comment to the Taken list!
Other OOC info:
This is just semi-private; I'm not restricting membership too much, but neither do I want to advertise it all over the place. It's basically a 'friend-of-a-friend' thing here as far as invites go, we're cool so long as you know people here.
I'm also not bothering with a rules post for this because it's pretty unnecessary and would just boil down to 'don't be a dick'. So. Don't be a dick to your fellow players. I am not a mod so much as just the person setting this stuff up and probably throwing out potential plot bones later if it seems like a good idea, but I will deal with personal disputes and things if I have to and I'd prefer that I don't.