GRASS je modulární systém:
| Administrativní moduly: | 19 | g.region, g.list |
| Rastr 3D : | 15 | r3.gwflow, r3.out.vtk |
| DPZ : | 24 | i.ortho.photo, i.pca, ... |
| Vektorové moduly: | 95 | v.net.steiner, v.build, ... |
| Rastrové moduly: | 135 | r.reclass, r.buffer, ... |
| http://grass.osgeo.org/wiki/GRASS_AddOns | (mnoho) | r.in.wms, v.trees, r.in.gdalwarp |