- LeafletJS - http://leafletjs.com/
- OpenLayers - http://openlayers.org/
- OpenLayers 3 Beta - http://ol3js.org/
- Modest Maps - http://modestmaps.com/
- Polymaps - http://polymaps.org/
- GDAL/OGR - http://www.gdal.org/
- RGeo - http://dazuma.github.io/rgeo/
- GeoDjango - http://geodjango.org/
- TurfJs - https://github.com/morganherlocker/turf
- Mapnik - http://mapnik.org/
- SimplerTiles - http://propublica.github.io/simpler-tiles/
- QGIS - http://qgis.org
- PostGIS (PostgreSQL) - http://postgis.net/
- Spatialite (SQLite) - https://www.gaia-gis.it/fossil/libspatialite/index
- MySql Spatial Extensions - https://dev.mysql.com/doc/refman/5.7/en/spatial-extensions.html
- Mongo Spatial - http://docs.mongodb.org/manual/core/geospatial-indexes/
- CouchDB spatial - https://github.com/couchbase/geocouch/
More complete list: http://opensourcegis.org/