Spy mod was created for multiplayer use with multiple forces. It boosts technologies of all forces (even those who are yet to be created*),when one of forces finish research. The purpose of this is to work with "every player in his own force" scenarios - so that players won't lag so far behind others in tech for long and hopefully won't get overrun by biters. Once one player will make technological breakthrough -> rest have easier path to follow.
Small changes concerning balance, gameplay, or graphics.