The original sources of MS-DOS 1.25, 2.0, and 4.0 for reference purposes

Raspberry Pi ARM based bare metal examples

The development kit for over a hundred z80 family machines - c compiler, assembler, linker, libraries.

A modern, scratch-built, open-source (GPLv3) alternative ROM BIOS for PC, XT, 8088 Clone or Turbo PCs.

Porting Richard Jones' FORTH to ARM; TAKE A PISS ON GITHUB

Forth for the ARM Cortex-M3

Improved Apple //c (ROM 4X) and Apple IIc Plus (ROM 5X) firmware.

A bootable 1 MB solid state disk for Apple ][ computers

ROM based March-U RAM test for the Apple II

R.T. Russell's BBC BASIC for Z80, with additional features by J.B. Langston

YAZ180 - Modern Single Board Z180 Computer

CP/M for the NABU Personal Computer using a compact flash adapter

Kick assembler personalized version of the C=64 rev. 781220 Dead Test + more

Minimal FORTH for bare-metal RPi, based on pijFORTHos

The big project that I am most likely to finish.

A generic opensource IBM XT BIOS clone

Double Dragon 2 jamma/arcade board sound diag program