Yeah, the Christian music festival, or the biggest one at least. Music includes Christian contemporary, pop, hardcore, punk, hippie and crusty folk, screamo, indie etc. No regulations. I haven't been to too many other festivals, but I've been told Cornerstone has a very great positive atmosphere, as the camp site is mixed with the stages and most people are outgoing and non cliquey, etc. Not sure how it compares myself, but I certainly enjoy the atmosphere.
The point of the fest is to glorify God, but they generally include any bands with Christian associations, even if the band doesn't have a Christian "purpose", y'know? Of course, any musician who has ever been authentic, does sing out of what he believes, so if you can't stand hearing any songs about Jesus or faith then don't bother coming. Luckily for all of us, the contemporary stuff stays to the main stage, and the underground stuff takes over the majority of the stages. There's also generator stages which pick up the little bands who just show up and showcase them. The fest covers the entire spectrum of bands. Most of those bands are terrible emo-pop or breakdown bands (it's a refined version of hardcore, y'know), but it's easy to shut them out as white noise by the end of the first day.
Anyways, I still find it worth going to. There's always a hobo camp with a couple handfuls of punks, anarchists, vandwellers, primitivists, etc. and they are super swell and all around pleasant. Psalters have not played in a while (because they play very little these days), but Jeremy who is a key member has his own anarcho-folk project called The Illalogical Spoon which is pretty sweet. You can check em out here:
theillalogicalspoon on MySpace Music - Free Streaming MP3s, Pictures & Music Downloads
I'm sure more of that cast will be showing up to do some of their own stuff.
Anyways, now you know.