GPXSee is a GPS log file viewer and map browser that supports all common GPS log file formats incl. the garmin img file format.
For mobile devices (smartphones, tablets) the Oruxmaps is also compatible with Garmin img tiles.
Locus can import the Garmin img maps into their map app, but unfortunately the map styles are not supported. Therefore I can't recommend to import the OFM maps in Locus app.