PICO-8 is perhaps the most popular of the fantasy consoles and if you are extremely quick, you can pick it up as part of the Itch.io Racial Justice bundle along with a ton of other development tools and indie games. PICO-8 is described as:
PICO-8 is a fantasy console for making, sharing and playing tiny games and other computer programs. It feels like a regular console, but runs on Windows / Mac / Linux. When you turn it on, the machine greets you with a commandline, a suite of cartridge creation tools, and an online cartridge browser called SPLORE.
It emulates a very limited virtual machine:
128x128 16 colours
4 channel chip blerps
256 8x8 sprites
Additionally PICO-8 has several built in tools including a sprite editor, sound editor, level editor and music editor, as well as tools for publishing and sharing your creations with out. The underlying programming language is Lua and is documented here. You can check out PICO-8 in action in the video below.