Goodgym combines volunteering with exercise to create a "double sense of smugness", as founder Ivo Gormley put it. He was frustrated with pointlessness of gyms; all that wasted energy from furiously stationary, runners, cyclists and elliptical trainees, and a lot of people paying but not going. Goodgym sends people on running errands to make visits to elderly or disabled people - helping the runners feel they're actually achieving something, and combatting the growing social isolation of people who can't get out much.
Goodgym was set up a few years ago as a social enterprise in London (Guardian coverage here) and went through the first Bethnal Green social impact accelerator. They now have over 300 runners and operate across London and others cities in the UK. I met Ivo at the Aging2.0 and Nesta event in London this week and was struck by the idea's brilliance, simplicity and his enthusiasm. See his TedX talk below: