Bike sharing is implemented more then some might think. In several major European cities there are bike-sharing projects, facilitated by the local government, such as Paris and Barcelona. For a small yearly fee and possibly a use-fee you can get bikes from almost anywhere in the city. There is also a shared bike project in Copenhagen, but this is mostly for tourist use and not available in winter.
Community Bike Workshops
Many large cities in Europe and the US have special Do-it-Yourself bike centers where you can come to fix your bike. These centers range from open workshops at squats to centers with professional volunteers that are open on a daily basis, often backed by a legal association, such as the Los Angeles based Bike Kitchen.
Free Bike Sharing projects
A few free bicycle sharing projects that span internationally exist in the world. One recent started project is bike-sharing.org. This website works much like CouchSurfing, where free requests can be sent and user trust is empowered by writing references for each other.