I've seen a few of these fantasy computers appear in the last few years and they are pretty interesting. PICO-8 is another example, but that one has a cost attached to it.
Here's how the developer describes it:
TIC-80 is a fantasy computer for making, playing and sharing tiny games.
There are built-in tools for development: code, sprites, maps, sound editors and the command line, which is enough to create a mini retro game. At the exit you will get a cartridge file, which can be stored and played on the website.
Also, the game can be packed into a player that works on all popular platforms and distribute as you wish. To make a retro styled game the whole process of creation takes place under some technical limitations: 240x136 pixels display, 16 color palette, 256 8x8 color sprites, 4 channel sound and etc.
You might be wondering why these exist and it's valid question! The way I see it is in two parts: fun and to learn. It's an interesting way to learn a little programming and fun for developers who like retro stuff, especially because of the hard limits imposed on people making stuff with it. It's also even more awesome that it's now open source.