Someone made an operating system for the NES

engadget.com:

You probably never saw the NES as a productivity machine, but some clever developers beg to differ. Hackaday and Ars Technica note Inkbox Software has released a graphical operating system, NESOS, for Nintendo's console. The mid-'80s technology restricts the OS to two apps (a word processor and settings) and eight 832-byte files, but you have an honest-to-goodness pointer, movable icons and customizable interface colors.

Inkbox primarily had to overcome the NES' very limited memory and storage. NESOS fits into just 48K, and the files have to sit inside the 2K of NVRAM that retains data when the console turns off. Graphics memory was a particularly large hurdle. Nintendo's system only has two sprite memory grids (one each for the foreground and background), and it can only display 64 sprites at any time — that's why many NES games flicker at busy moments. The creator had to combine sprites into larger shapes.

The project is available in a ROM that you'll likely use through an emulator (unless you make your own cartridge). You won't be writing a novel in NESOS. The memory prevents any kind of substantial content creation, and typing with the NES controller involves very slowly cycling through characters. This is more about defying expectations, and it's significant that Inkbox didn't have to modify the console to achieve its feat.