kmap
Builds Garmin maps from OpenStreetMap
...Two styles are built in, modelled on Openstreetmap and OpenTopoMap, and kmap can reuse the look of a map you own where its licence allows. Profiles keep a separate set of build settings for each device.
kmap runs as a full-screen terminal interface, and every feature is also available from the command line. Map data comes from Geofabrik's OpenStreetMap extracts, updated daily; the tools kmap needs are downloaded on first run.