The 2600 VCS is really interesting. It didn't even have a framebuffer, so painting pixels was done scanline by scanline and you had to be done with your scanline in a certain amount of CPU cycles, which meant you had to count them and know which instruction took how long.

It only had 128 bytes RAM, that's bytes, not KB.

A real technical marvel is the chess game for the 2600. Since the sprite capabilities were so primitive, they couldn't even draw all pieces in a single scanline, they had to alternate scanlines so that they could even draw all chess pieces, and that's not even mentioning the fact that they somehow made a chess playing algorithm work in 128 Bytes of RAM.