For regular Android Smartphones, you can get an Elm plugin to the OBD connection on various cars, then many different apps for your Smartphone from Google play.

Plugs into car's OBD2 diagnostic connection. ($9)..
http://www.amazon.com/Version-Bluetooth-Multi-Language-12Kinds-Android/dp/B00N2K6M2A

Apps for above...
Elm Electronics - OBD Software

[The technical information and chips for the above - for technical types]...
Elm Electronics - OBD ICs