FuryBand is a great game to mod. The engine makes it very simple to do so. If you have programmed a mod, please email me, so I can add it to my list.
Here is a current list of Modules for FuryBand
Half Life RPG
To read more about this mod, please see its page here
GerBand is a fun module that adds a lot of nethackish elements, along with a lot of new foods. It is a lot of fun. You can download it here
Zop's FurybandTo read more about this, please see its page: here
This is a straight port of Tome to the Fury-Engine
You can download modules for FuryBand here