I use the capo on the second fret, and then play an open Gmaj form, which is an Amaj. It's a very nice sounding chord.

I often use a capo on the third fret when playing a blues shuffle in G, as I get considerably less hand fatigue this way compared to the barre chord.

A lot of folks tune to an open D and use a capo in the second fret for open E playing, but I prefer to just use the open E tuning.

The combination of open or alternate tunings and the capo opens up a bunch of possibilities...

Fire, the wheel, and the I IV V -- foundations of civilization.