Help needed: FOSS for public transportation systems

Do you know of free and open source software (FOSS) for managing public transit (public transportation) systems? Especially small, bus-based systems. Perhaps I don’t know the lingo well enough, but all I can find are expensive, proprietary systems. You would think there was a need.

As in earlier requests, pointers to good association or government sites, or thoughtful blogs, are also welcome.