Before going to the bar, I made a commitment on Facebook to make a small extra charitable donation if I did not strike up a conversation with an attractive woman within 60 minutes of arrival (with the intention of increasing the donation amount each time in case of failure. Note that I did not choose a donation to a cause I disagree with, because that would have been adding a source of additional stress in an already stressful situation. The actual motivator here was more "not fail publicly in front of my FB friends," since I'll end up donating to AMF or GiveDirectly eventually regardless.)

Why not Beeminder?