OsmAnd - Global mobile map viewing and navigation for online and offline OSM maps
QGIS - QGIS is a desktop geographic information system, or GIS.
MAPS.ME - Fast, detailed and completely offline maps for mobile devices
GRASS GIS - GRASS GIS is a free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization.
HERE WeGo - HERE WeGo - Maps - Routes - Directions - All ways from A to B in one
SAGA GIS - SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS)...