http://www.tigrs.org/Now, I'll let Gameproducer take over:
http://www.gameproducer.net/2007/03/16/tigrs-the-independent-game-rating-system/Quote:
TIGRS is different from ESRB in 2 major ways. First of all: it’s free. ESRB ratings cost a too big pile of money for casual games to get a rating, with TIGRS everybody can get their game rated. Secondly: it’s rated by developers.