From publisher blurb:
Successful adventuring is a cooperative exercise. Parties who cannot work together, or do not at least have complementary skills and abilities, do not often last. However, the d20 System provides only a few rules which actually allow for in-game modifiers based on cooperative actions.
Options such as the aid another action are useful and realistic, but they are too few and lack in colour and excitement. When aiding another character on a skill check, you can provide your ally with a +2 bonus to their check. That's nice, but it's not terribly interesting.
Party Synergy provides rules for many specific situations in which characters can cooperate (called synergy maneuvers), with specific game effects. It takes the concept of skill synergy to a new level. When characters perform certain actions in concert, they receive benefits that exceed the simple sum of the parts.
The central mechanic of the party synergy system is the new Share Knowledge skill. This skill, in addition to giving access to the various synergy maneuvers, allows one character to coach and train another in a particular skill, giving the other character a bonus that lasts several rounds, or even allowing the other character to increase his ranks in the skill – without having to advance a level.
In addition to the Share Knowledge skill, this 8-page PDF presents 13 synergy maneuvers, from the defensive Shield Wall, to the offensive Phalanx, to the grueling Superior Forced March.