I don't really like the way the PHB does unarmed combat. It seems to kind of pieced together and not very desirable. I wanted to create a system that was simple, yet had enough advantages to make an unarmed specialist a little more reasonable.
Unarmed combat depends on how many proficiency slots are put into it.
Everyone has this basic unarmed combat ability. They can punch 1/round.
This allows the brawler to punch with both hands in a round without penalty. 2/round. This counts as a melee weapon, so fighter-types get their level advancement (2/3/4) in attacks.
With specialization comes extra benefits. You get an extra +1/2 attacks with each hand, so a fighter would get (3/4/5) attacks. You also get the standard +1/+2 to hit/damage bonus.
Plus, if the specialist wears anything less than leathor armor, he can use an attack to get the parry bonus against another attack. So, if a 6th level fighter normally has AC:8, he can give up 1 attack to get AC:4 versus one attack. He can use as many attacks as he wants in this manner, even doubling up two of his attacks against a single attack.
Punching is always speed 2 and does 1d2 damage.
Also, for unarmed combat purposes, punching is just a generalized term for any unarmed damage method. It could also be kicking, head-butting, elbowing, etc. Creative ideas just make this style that much cooler.