The Tulsa River Parks Authority has "Tulsa Townies" bicycle stations at two places on the River Parks.
You pick out your bicycle and then use your credit card to unlock it from the unattended solar powered station.
The bikes are free if you return them in 24 hours. If you don't you just got yourself a $100 bicycle.
I've never used them but they get sold out on nice weekends. I think that it is a great idea.