Vouch is a mobile app that analyzes users' Facebook graph to connect them to all the singles on Facebook that they have common friends with. It also helps users that are already in relationships play matchmaker and anonymously match their single friends (we keep their identity a secret until they are ready to reveal themselves as the cupid). This eliminates the fear, from the matchmaker, of making a bad match and being blamed by their friends in the aftermath - allowing for all the benefits if the match works out, and none of the risks if it doesn't.
The entire system is built into a game that encourages users to re-engage on a daily basis - whether single and looking for a date, or in a relationship and just playing matchmaker; the average user from our beta launch checks back every other day.
We plan to eventually integrate the matchmaking into Facebook directly and award users scores for making successful matches, which they can then publish on their walls (free publicity).