Hollaback! Every woman who walks down the street in a city knows what it's like to face street harassment and how disempowering it can be. This wonderful app lets you hollaback, whether it's telling the world what happened, or, if you feel safe enough, taking a picture of your harasser and uploading it to the site. Street harassment teaches us to be silent, to look the other way, but we are told we shouldn't put up with harassment in the workplace or at school--why should we on the streets?

CauseWorld A little like Foursquare, Causeworld lets you check into stores and places and earn 'karma' points, which can then be used to donate to causes that you believe in like girls' education, vaccines, or saving the dolphins. You can also link up your CauseWorld activity with your Facebook for a wider impact.

Congress This brilliant app is like having the US Congress in your back pocket (without the bribes, of course!)-- find out about the latest bills and laws, see how the votes were cast, call your Congresspeople automatically or track their social media output, track pieces of legislation you're interested in, and share all of this information with your network. Be an active and informed citizen with this app.

Find Green This app helps you find green and sustainable businesses quickly and easily, as well as pointing you to environmental news and tips.

Ushahidi Ushahidi is a super-cool app that works with the Ushahidi platform for information collection, visualization and interactive mapping. It's been and is being used for everything from election monitoring, such as the 2009 Indian general elections, to tracking crisis responses, such as the post-earthquake response in Haiti.