Pledger is an app aimed at enabling micro-volunteering by listing NGO's or NPO's with causes ("deeds" in Pledger parlance) by location. The user of the app can simply browse a list or map of deeds in his/her area, and volunteer for a deed. Pledger is still in the development phase and has not launched yet, but you can find out more at the official website.
The Pledger mascot is (currently) the "Pledger Pig". Keep an eye out for #PledgerHeroes as they volunteer for events when Pledger is launched.