This hand and inexpensive tool is what every home brew kegger should have in the toolbox.  It's really useful for all the most common fittings that you are likely to see in the draft beer world.
 
This new 7 in 1 tool is also suitable for duotight fittings so it's been improved since the older 5 in 1 tools.
 
This handy tool is exactly what you need to fit numerous dispensing applications:
1. Nut behind your taps (27mm Spanner)
2. Ring collar connecting your tap to the shank.
3. Attaching your type 30 Regulator to your CO2 Bottle
4. FFL fitting to tighten/undo an MFL connection. (e.g. Barbed fitting on CO2 Regulator)
5. Last but not least, the handy dandy bottle opener.
6. Remove 8mm tubing from duotight fittings
7. Remove 9.5mm tubing from duotight fittings.