An Operating System for Z80 computers, written in assembly
Zeal 8-bit OS is an operating system written entirely in Z80 assembly for Z80 computers. It has been designed around simplicity and portability. It is inspired by Linux and CP/M. It has the concept of drivers and disks while being ROM-able.
The Amsterdam Compiler Kit is a cross-platform compiler and toolchain suite that is small, portable, extremely fast, and extremely flexible. It targets a number of low-end machines including the Z80, 8086 and 80386, but there are many other code generators available. It supports several languages, including ANSI C, B, Pascal and Modula-2, and contains integrated runtime libraries including a libc.
cool-retro-term is a terminal emulator which mimics the look and feel of the old cathode tube screens. It has been designed to be eye-candy, customizable, and reasonably lightweight.
Old x86 IBM PC emulator