Yeah it's a flash-based Facebook Game. You can have a party of up to 4 and you can include characters your friends create. Friends can watch you play with their characters and help out in a peripheral manner.
Here is the link to the facebook page, not the app.
http://www.facebook.com/?sk=lf#!/HeroesOfNeverwinter
Everyday they announce openings into the BETA which seem to fill instantly. I tried for a few days before finally being on FB the same moment they announced openings, then WHAM!
I also joined this FB group:
http://www.facebook.com/?sk=lf#!/gro...9842794043420/
Which has a very helpful FAQ/Guide posted.