Widgets and more:
Chess Scripts
DHTML Chess
Chess FEN viewer
Chess Blindfold Trainer.
Chess scripts
The above not just for Macs.

All OS Systems: Mac, Linux, Windows:
Chess widgets » Browse widget gallery for Chess widgets
What you can download
PowerOnGames.com Play Chess
Strategy Chess (RSS)
Strategy Chess (Google Gadgets (Windows)

Macintosh:
Apple - Downloads - Dashboard Widgets - Chess
Chess with variants , Crazyhouse, Suicide, Losers, Atomic and more.

JavaScript:
Chesstr.com - Chess Widgets