This is not a joke! Leave the Clipper Card, Muni pass and those crumpled $1 bills at home tomorrow. To celebrate Muni’s 100th anniversary, service (aka rides) will be free, free, free from 5:00 a.m. on Friday, December 28 until 5:00 a.m. on Saturday, December 29. San Francisco Municipal Transportation Agency is inviting everyone to “Come on and Take a Free Ride” on any and all Muni vehicles -- yes, even cable cars.
According to the SFMTA Press Release, Muni was the "first major, publicly owned, land-based transit agency in the United States". The story of how Muni came to be typifies the true spirit of San Francisco. In 1909, San Franciscans, angered by the monopoly held by United Railroads on the city's transportation systems, voted to approve bond measures to create a municipal streetcar line. Three years later, Muni's Opening Day ceremonies were held on December 28, 1912 at Geary and Kearny streets and streetcar service on the A and B lines was inaugurated.
SFMTA created a special website commemorating Muni's 100th Birthday where you'll find old-timey photographs (including several amazing pictures from before and after the 1906 Earthquake and Fire), a calendar of Centennial Celebration events and a well-researched history of Muni. All good stuff.
P.S. Don't forget that Muni is also offering free rides after 8:00 p.m. on December 31st to help you safely ring in 2013. This is what Muni's New Year's Eve service will look like: