Free Software packages using GEOS

• ​MapServer (C API)
• ​OGR (C API)
• ​PostGIS (C API)
• ​R sf (C API)
• ​QGIS (C API)
• ​GeoDjango (C API)
• ​geoPHP (PHP API)
• ​gogeos (C API)
• ​GRASS (C API)
• ​INGRES (C API)
• ​MapGuide Open Source
• ​MapWindow GIS (C API)
• ​MonetDB (C API)
• ​node-geos (C++ API)
• ​osgEarth (C++ API)
• ​PDAL (C++ API)
• ​rgeos (C API)
• ​RT Topology Library (C API)
• ​Shapely (C API)
• ​SpatiaLite (C API)
• ​Zgel (Ruby API)

Proprietary packages using GEOS

• ​Autodesk MapGuide Enterprise
• ​Cadcorp SIS
• ​FME

Software that used to use GEOS

• ​osm2pgsql <= 0.92 (C++ API < 3.6) (0.94+ uses Osmium)
• ​Osmium Library (C++ API < 3.6) (now uses GDAL)