The KOMOS is a handy and inexpensive tool that every homebrew kegger should have in their toolbox.  It's really useful for the most common fittings that you are likely to see in a home draft system, and Duotight users will appreciate the handy removal tool for 8 mm and 9.5 mm fittings.
Functions:
CO2 Regulator Nut Spanner
Shank Hex Nut Spanner
Faucet Coupling Ring Pin Wrench
Flare Swivel Nut Spanner
8 mm Duotight Removal
9.5 mm Duotight Removal
Bottle Opener