From TechCrunch:

 Democracy doesn’t work if you don’t vote, so Votizen helps make sure your friends do. Log in with your Facebook, Twitter, or LinkedIn accounts and you’ll see who in your network is registered to vote. Pick an election and the candidate you support, and Votizen gives you a list of friends who support that party and are eligible to vote in the race. That way you can remind them to cast theirs or band together to campaign for who you want to win.

Votizen is intended to be used as a Get Out the Vote tool, and it makes it very easy to do so in a partisan way.  The League itself does not endorse candidates or parties, but we encourage our members to be active politically, including in partisan politics, if that is their desire.  Above all, we encourage citizens to use every means at their disposal to build the habits of registering to vote, and of voting, among their friends and associates of any party or of none.

Full article from TechCrunch, with a couple other apps