TIC-80 - TIC-80 is a fantasy computer where you can make, play and share tiny games.
PICO-8 - Lua-based fantasy console for making and playing tiny, computer games and programs.
Pyxel - Retro game engine for Python inspired by fantasy consoles.
Voxatron - Voxel-based fantasy console
8bitworkshop - Online IDE for Atari 2600 development based on Javatari.
nano JAMMER - Full-featured fantasy console that runs entirely in the browser and supports Google Drive