If you don't know where to look for software try the "Extras" (SYS:Extras) folder first, it represents AROS' "contrib" archive (DOpus, Quake, Doom, AmiChess, ...).
Try these sites:
- AROS main software archive
- ported games and other programs by Yannick
Some AROS projects are hosted on sourceforge.net, try searching there.
"Bleeding edge" news about latest software releases or developments can be observed at aros-exec.org
As always, Google is your friend.