The Barbarian Group's Gastrodamus is a free iPhone [iTunes link] and Android app that aggregates local trucks' Twitter feeds.
Cities covered at this point include New York; Los Angeles; Portland, Oregon; Washington, D.C.; San Francisco and Boston. Unlike other apps, which use methods ranging from GPS to self-reporting, Gastrodamus is completely based on Twitter. If a truck's feed mentions a location, it gets listed for that day. If not, it doesn't.
The app, developed by the agency as a side project, is a work in progress. The Barbarian Group is asking users to send suggestions for new food trucks. One major oversight is the app's inability to find the food truck closest to you. There are other glitches as well: Participating trucks that clearly state their location, like Korilla BBQ and Van Leeuwen Artisan ice cream, don't show up in the "most recent" feed and get a "couldn't locate this truck" notation.
Still, it's hard to complain about a free app, especially one that provides some solid info.
Below are five other mobile apps that can help you locate food trucks:
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