The Windows/Linux Openmtbmap Maps Can be found Here
Maps for Mac OSx can be found Here
Programs to Display the Openmtbmap
Besides being shown on (nearly) all Garmin GPS devices - most People will use Garmin Basecamp (v3 or later) or Garmin Mapsource to show the maps on their Desktop and plan tours/trips.
For anyone on the good side of earth Openmtbmap.org maps are also correctly shown in Qlandkarte_GT - QLandkarte_GT is compatible with all big OS (Linux, MacOSx and well Windows too). Linux users can alternatively install Mapsource 6.13.6 in WINE. The .exe files can be unpacked with 7zip.
For Linux/Unix users there is also a script to unpack the maps, and automatically create a gmapsupp: https://github.com/btittelbach/openmtbmap_openvelomap_linux
Mapsource - I wouldn't use any version but 6.16.3. Mapsource versions 6.14 to 6.15.6 are complete junk, if you use it, please update. Also note that Mapsource versions prior to 6.16.1 do not show all ways and pathes so they are not really usable. Mac OSx users please use Qlandkarte GT or convert maps and use Basecamp 3 or Roadtrip. Note there are readily converted maps available for most countries at the end of this page.