Actually written in Assembler to it. You had to squeeze the entire code and the graphics to 16k (K, that is 1024 bytes!). Rendering the screen was directly poking values to the hardware. Great piece of hardware
Two very common machines from the era were the ZX spectrum and the TRS-80. But there were dozens - Kaypro, Osborne, MSX, the Nintendo Gameboy... the Z80 was used in lots of machines. Chips based on the Z80 are still used in embedded systems today.
I built a retro-computer this year using a Z180, which is a Z80 (minus undocumented behaviours) core with a handful of useful peripherals built in. They're still actively manufactured and sold.