From SF Bike Coalition:

Celebrate Earth Day in the Heart of San Francisco, the “Greenest City in North America.” New this year, in collaboration with community groups around the City, the San Francisco Bicycle Coalition has been organizing a series of skill-share Convivios aimed at encouraging at-risk youth and working-class immigrants to get in the saddle. Volunteer mechanics assist their fellow members of the community in refurbishing recovered and donated bicycles which they take home! Our intro to Safe Bicycling Class as well as basic safety equipment is also provided. Drop by and take a look or help out at the Convivio during the Earth Day SF celebration.

More details on Earth Day SF at earthdaysf.org