There are three feats in OA that help grappling: Improved Grapple, Choke Hold, and Earth's Embrace. They all seem to be designed with monks in mind.
CHOKE HOLD [GENERAL]
You have learned the correct way to apply pressure to render an
opponent unconscious.
Prerequisites: Improved Unarmed Strike, Improved Grapple, Stunning Fist.
Benefit: If you pin your opponent while grappling and maintain the pin for 1 full round, at the end of the round your opponent must make a Fortitude saving throw (DC 10 + 1/2 your level + your Wisdom modifier). If the saving throw fails, your opponent falls unconscious for 1d3 rounds.
EARTH'S EMBRACE [GENERAL]
You can crush opponents when you grapple them. This feat is called tsuchi-do in Rokugan.
Prerequisites: Improved Unarmed Strike, Improved Grapple, Str 15+.
Benefit: While grappling, ifyou pin your opponent, you deal critical damage (double normal unarmed damage) each round that you maintain the pin. You hold your opponent immobile as normal, but you must also remain completely immobile, giving opponents (other than the one you're pinning) a +4 bonus on attack rolls against you (but you are not helpless).
IMPROVED GRAPPLE [GENERAL]
You are skilled in martial arts that emphasize holds and throws.
Prerequisite : Improved Unarmed Strike .
Benefit: If you hit with an unarmed strike, you deal normal damage and can attempt to start a grapple as a free action without provoking an attack of opportunity. No initial touch attack is required . You can deal normal damage while grappling, rather than subdual damage, without suffering a penalty on your grapple check.
Normal: Characters without this feat make a melee touch attack to grab their opponent and provoke an attack of opportunity when doing so .They also suffer a -4 penalty on their grapple checks when trying to inflict normal damage in a grapple.