I'm looking forward to the next versions of Rev and Dashcommand. These applications connect wirelessly to the cars computer via an accessory, such as Kiwi WiFi or OBDKey, that is plugged into the OBD II port under the dashboard and are able to display, diagnose, and log information from the ECU. In addition to displaying real time gauges of speed, RPM, boost, throttle, fuel trim, MPG, etc, they can also reset the ECU's error codes.
The next revision of these apps will integrate trip information to include mileage as well as other information. I'm presently using Rev, which is great, with my Kiwi WiFi but the next version of
Dashcommand looks very impressive.
Here are some screenshots of the hopefully upcoming Dashcommand update: