I have been using a cheap (<$20) OBD-II dongle in my car for over a year now. The Torque app[1] has an impressive feature list and constant updates. I use it with my tablet inverted on the dashboard during night-driving for giving me a heads up display[2]. It's also great for things like acceleration graphs, tracking stats over the internet, and keeping check on the engine's performance/mpg.

[1] https://play.google.com/store/apps/details?id=org.prowl.torq... [2] http://www.youtube.com/watch?v=4OPH7ZJJHV8

Yes, Ford's OpenXC uses the OBD-II port, and talks to Android through an Arduino.

Website: http://openxcplatform.com/

OpenXC post on HN: http://news.ycombinator.com/item?id=4745039

In the mobile space, I believe there are some connectors for vehicle monitoring tools and the like -- for tracking performance data on the track or to provide supplementary info to dashcam programs. I don't know of anything standalone like this.