Gosmore is an OpenStreetMap navigation application. It can display the map in 2D and 3D. It also provides searching and turn-by-turn routing capabilities. All the data is stored offline in it's own binary format.
Error while downloading maps (Error: 7-Zip cannot find the code that works with archives), UI is primitive, did not create a Windows uninstall entry so I had to uninstall it by hand. The back-end may be very nice, but I never got far enough into the program to be able to use it, let alone want to.