gamma tester 

A user of new software or equipment, who must deal with the bugs that were not eliminated in beta testing.

(Derivation: Gamma is the next Greek letter after alpha and beta.)

I'm going to wait a while before getting Windows Vista; I remember the problems people had with XP and Service Pack 2 when they came out, and I don't want to be a gamma tester.

gamma tester by Aaron of Minneapolis February 1, 2007

Gamma Tester 

Someone who receives their Amazon game pre-order early, so they can give feedback to the developers before the official release date.

I got Yakuza Kiwami on the 26th of August even though it was officially released on the 29th. I guess they wanted me to be a gamma tester for the game.

Gamma Tester by Eddiehimself December 9, 2017