The Bay Area's has several public transportation networks. There are four independent rail systems (described below). Unfortunately, the systems are independently operated, so you may have to purchase separate tickets when you switch between the different systems. For a unified map of the rail systems, see SiliconValleyMap.org.
Google Maps allows you to find directions using public transportation mode around the Bay Area. It will tell you precisely which trains or buses to take for you to get to your destination.
Ride sharing allows you to very quickly request a ride from your mobile device and is a convenient alternative to a traditional taxi. Silicon Valley is home to the biggest ride sharing platforms Uber and Lyft.
Zipcar provides automobile reservations to its members, billable by the hour or day.
Company shuttles are also common to complement public transportation. Google has one of the largest private bus networks in the area. There are also several startups in the private shuttle market: