Operating systems & system software, reimplemented
Operating systems, compatibility layers, firmware and system software, reimplemented.
Advanced Mac Substitute
Classic Mac OS (68K Toolbox)
Reimplementation of the 68K Mac OS Toolbox that runs classic Mac applications without Apple's ROM or system software.
AROS Research Operating System
AmigaOS 3.1
Portable reimplementation of the AmigaOS 3.1 APIs that runs natively on PCs and as a replacement Kickstart on Amigas.
Asahi Linux
Apple Silicon Macs (M1/M2 hardware)
Project that reverse engineers Apple Silicon hardware, including its GPU, to run Linux natively; m1n1 is its bootloader and research tool.
Atmosphère
Nintendo Switch Horizon OS components
Custom firmware that replaces many Horizon OS system modules and the kernel with open reimplementations.
Basilisk II and SheepShaver
68k and PowerPC Macintosh
Maintained fork of the Basilisk II (68k) and SheepShaver (PowerPC) Mac emulators, which need an original Mac ROM.
Box64
x86-64 Linux userland binaries
Dynamic recompiler that runs x86-64 Linux programs on ARM64 and RISC-V, forwarding library calls to native libraries.
Cromwell
Original Xbox BIOS
Free, legal BIOS replacement for the original Xbox, written to boot Linux without Microsoft code.
Cxbx-Reloaded
Original Xbox kernel and system software
Xbox emulator that reimplements the console's kernel and libraries at a high level so games run on Windows.
Darling
Apple macOS (Darwin userland)
Translation layer that runs macOS command-line and some GUI programs on Linux by reimplementing Darwin and macOS frameworks.
EmuTOS
Atari TOS
Free replacement for the Atari ST TOS ROM, usable in emulators and on real Atari and compatible hardware.
Executor
Classic Mac OS Toolbox
Classic Mac emulator that ran 68k Mac applications by reimplementing the Macintosh Toolbox instead of using Apple ROMs.
FEX
x86 and x86-64 Linux binaries
Usermode x86 and x86-64 emulator for ARM64 Linux with a JIT and library thunking, used to run PC games on ARM.
FreeDOS
MS-DOS
Complete MS-DOS-compatible operating system for running classic DOS software and games.
Haiku
BeOS
Open-source operating system that recreates BeOS and stays compatible with its applications.
Infinite Mac
Classic Mac OS and early Mac OS X
Browser-based collection of classic Macintosh systems running in WebAssembly ports of Basilisk II, SheepShaver, Mini vMac and others.
MINI
Wii IOS (Starlet firmware)
Minimal open replacement for the Wii's IOS firmware on the Starlet coprocessor, part of the BootMii project.
Mono
Microsoft .NET Framework
Open-source implementation of the .NET runtime and class libraries, built from the ECMA standards; development has since moved on.
NTFS-3G
Microsoft NTFS file system
Read/write NTFS driver built from reverse engineering of the on-disk format, running in user space via FUSE.
OpenBIOS (PCSX-Redux)
PlayStation BIOS
Open-source replacement for the original PlayStation's BIOS, developed with the PCSX-Redux emulator.
osFree
IBM OS/2
Effort to build an open-source OS/2-compatible operating system, starting with its user-mode parts.
ReactOS
Microsoft Windows NT (Server 2003 era)
Free operating system written from scratch to be binary-compatible with Windows NT drivers and applications.
Samba
Microsoft SMB/CIFS and Active Directory protocols
Reverse-engineered implementation of Windows file and print sharing and Active Directory domain services.
System7
Apple Macintosh System 7
Experimental bootable reimplementation of classic Mac OS System 7 for x86 PCs, documented through reverse-engineering notes.
v86
x86 PC hardware
x86 PC emulator that JIT-compiles guest code to WebAssembly and boots DOS, Linux, BSD and other systems in the browser.
Wine
Microsoft Windows API
Compatibility layer that reimplements the Windows API so Windows programs run on POSIX systems without a Windows licence.
xemu
Original Xbox
Low-level original Xbox emulator based on QEMU that runs the console's own system software.
Xenia Canary
Xbox 360 kernel and system software
Xbox 360 emulator that reimplements the console's kernel and system libraries at a high level; Canary is the actively updated fork.