You may remember Akoha, a startup which launched at the 2008 TechCrunch50 conference which uses “mission cards” that friends pass to each other along with a mission ( i.e. give someone a book or buy someone a meal.) The idea is that users will socialize their missions, using your social graph to compete against friends and determine how your missions performed.

See the rest here:
Akoha Launches iPhone App To Help Users Socialize Missions