There is very cute micro handheld (like Sega VMU or Nintendo Pokemon Mini or Sony Pocket Station on steroids) called µGame.
It is based on Atmel SAM ARM (ATSAMD21, 48mhz, 32kb ram, 2mb flash, 128x128 LCD, 8bit mono audio). Main developing platform is Python (CircuitPython/MicroPython) but it is ARM so C, C++ etc is possible too... It works on Nokia battery for hours.
How it looks like:
More specs here:
https://www.tindie.com/products/deshipu ... nsole-kit/
Soon there will be case + buttons (I am case designer).
There will be website with forum in future too!
Please join Discord, Hackaday maybe you can do game, app, case modding...