EVERYONE SHOULD HAVE ONE!
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: