Beeminder comes to mind when thinking about losing money when you don't hit your goals (goes to the company). I've been too afraid to try since I'm a student with loans, but maybe it's time.
Actually the first derailment is $0 so if you're extra poor then you'll be very motivated to not derail even once, in order to prevent having to ever risk actual money.
And it can't hurt to try because if you do derail with the initial $0 at stake you'll have a chance to abort before there's any danger of losing your first $5.