GRASS GIS is free software,
anyone may develop his/her own extensions (addons). The addons listed
here are currently not part of the core software package.
Addons can easily be installed in your local GRASS GIS installation
through the graphical user interface (Menu - Settings - Addons
Extension - Install) or via the g.extension command.
How to contribute?
See instructions here: How to create a GRASS GIS addon.
