Carman has 2 abstraction layers. The first one is in libobd or the old obdlib(python) that deals with the obd communication itself and support ELM and ozen based scantools. The second layer was added on the 0.7 version with a daemon that collects data from GPS and OBD, save them to build a trip log and send them though D-Bus to the UI. The code is GPL as well and it is available at the garage's svn (carman project).