from SRD
Disarm(4) [Varies][AoO: Yes]
Description: The character and an adjacent target make opposed attack rolls with the their respective weapons. If the weapons are different sizes, the opponent with the larger weapon gets a bonus on the attack roll of +4 per difference in size category. If the target is using a weapon in two hands, he gets an additional +4 bonus. If the character beats the target, the target is disarmed. If a character attempted the disarm action unarmed, the character now has the weapon. Otherwise, it drops to the ground at the target's feet. If the character fails, then the target may make an attempt to disarm the character as an immediate, free action.
Note: A target wearing spiked gauntlets can't be relieved of the gauntlets by a disarm action. A target using a weapon attached to a locked gauntlet gets a +10 bonus to any disarm attempt made by an opponent.
This action substitutes for a melee attack, not an action. As melee attacks, it can be used once in an attack or charge action, one or more times in a full attack action, or even as an attack of opportunity.
Strike a weapon [Standard][AoO: Yes]
Description: A character can use a melee attack with a slashing or bludgeoning weapon to strike a weapon or shield that a character's opponent is holding. The attacking weapon must be no more than one size category smaller than the weapon attacked. (Treat a buckler as Small, a small shield as Medium-size, a large shield as Large, and a tower shield as Huge.) Doing so provokes an attack of opportunity from the opponent because the character is diverting it's attention from the opponent to the opponent's armaments.
Then the attacker and the defender make opposed attack rolls. If the attacker wins, the attacker has made a successful attack against the weapon or shield.
Trip an opponent [Varies][AoO: No]
A character can try to trip an opponent as a melee attack. A character can only trip an opponent who is one size category larger than a character, the same size, or smaller.
Making a Trip Attack: Make a melee attack as a melee touch attack. If the attack succeeds, make a Strength check opposed by the defender's Dexterity or Strength check (whichever ability score has the higher modifier). A character gets a +4 bonus for every size category he is larger than Medium-size or a -4 penalty for every size category he is smaller. The defender gets a +4 stability bonus on his check if he has more than two legs or is otherwise more stable than a normal humanoid. If a character win, a character trip the defender. If a character lose, the defender may immediately react and make a Strength check opposed by a character's Dexterity or Strength check to try to trip a character.
A tripped character is prone. Standing up from prone is a move-equivalent action.
A character may make a trip attack against a mounted opponent. The defender may use his Ride skill in place of his Dexterity or Strength check. If a character succeed, a character pull the rider from his mount.
This attack form substitutes for a melee attack, not an action. As a melee attack, it can be used once in an attack or charge action, one or more times in a full attack action, or even as an attack of opportunity.
