There is apparently a Gamebuino emulator someplace, not found it yet.
Doesn't seem terribly complex: Fundamentally, it's an Atmega with certain devices on certain pins, so you could probably don't need a Gamebuino specifically, an Arduino Uno or clone thereof should work.
Well, it's not exactly a Gamebuino but I did get the 5110 display and an Arduino clone. Kinda strawberry floated up by getting a 28 pin version of the chip, though, so I won't be running any Gamebuino software for a while yet.
Trying to. The physical connections are a bit confusing because the chip pins aren't numbered the same on the actual chip as they are on the arduino, and there's a deficit of pins on the through-hole version of the Atmega vs the 32pin version used in the Gamebuino proper anyway.
Learning a lot from the attempt though, which is the main thing.
Definate issue with the lack of battery circuit, though. It runs for about 4 seconds before conking out because A6 is just floating in the 28pin version of the ATmega and I haven't yet found the toggle to turn off battery checking.