Wikipedia
MoNav
MoNav (short for MObile NAVigation) is a free, car navigation system with GPS tracking, realtime routing engine. It uses data from the OpenStreetMap project. It supports multiple platforms and supports car, foot and bicycle navigation.
The software includes a local navigation daemon and a client. There is also a preprocessor, that converts OpenStreetMap data to data usable by the daemon, but the preprocessor does not need to run on the navigation unit. It is written in C++ using the Qt toolkit (for the non-graphical parts as well). It is maintained as a project in Google Code using the Mercurial version control system.