osFree Janus is a project to create a complete, open-source, compatible reimplementation of the classic 16-bit Microsoft Windows 3.0 operating system. This is a full clone of the Windows 3.0 environment, not just its kernel, developed as part of the osFree project.
The goal is to build an independent, modern reimplementation of historical Windows, including the kernel (KERNEL), graphics subsystem (GDI, USER), system drivers, and core components, capable of running both standalone on "pure" DOS and within a Virtual DOS Machine (VDM) session.
This project is an attempt to reimplement the 16-bit Windows kernel for use in VDM and standalone environments. Development heavily utilizes code from the TWIN, WINE, ReactOS, and HX-DOS projects. The reconstruction of the internal kernel and system structure relies significantly on Matt Pietrek's "Windows Internals", Andrew Schulman's "Undocumented Windows", and Daniel Norton's "Writing Windows Device Drivers" books.
- Complete Windows 3.0 clone – not just a kernel, but full GDI, USER, drivers
- Dual environment support – runs on pure DOS or inside a VDM session
- Independent reimplementation – no underlying Win32 or XFree required
- KRNL286/KRNL386 kernels – start autonomously from real mode DOS
- Compatibility with existing Win16 apps – aims to run original software
- Built from proven open‑source bases – TWIN, Wine, ReactOS, HX-DOS
The original OS/2 used a largely unmodified Windows, so this project can be considered a reimplementation of classic, "vanilla" Windows 3.x. This means most code is written to run without any underlying system (e.g., Win32 or XFree). The KRNL286/386 kernels must start from pure DOS and operate autonomously.
Most initialization code and the module manager are derived from HX-DOS, which serves as the starting implementation base.
Most other API functions are taken from Wine and TWIN, depending on the difficulty of porting to a pure 16-bit environment. Many functions have been ported back to a pure DOS 16-bit environment.
The project is at a very early alpha development stage. The graphics subsystem (GDI) is not yet implemented. User interface library (USER) now has a lot of working stuff. Most higher-level DLLs are also implemented on some limited level.
The first goal is to correctly launch a simple system application, such as WinVer, Clock and so on. This requires the kernel (KERNEL) to correctly load and initialize drivers (system, mouse, keyboard) as well as GDI.EXE and USER.EXE.
The target Windows version is 3.0.
The project includes reimplementations of all key Windows 3.0 system components:
| Directory | Description |
|---|---|
applications |
Standard Windows apps – mix from TWIN, Wine, ReactOS, MS File Manager |
resources |
Icons, bitmaps, cursors from TWIN, fonts from Wine |
dlls |
Standard Windows DLLs |
docs |
Distribution documentation |
dosx |
286 DPMI Host and Extender (not yet implemented, HXDOS used as a base) |
drivers |
Standard Windows/DOS drivers |
include |
Include files (reference only – OpenWatcom headers are used) |
kernel |
KERNEL.EXE / KRNL286.EXE / KRNL386.EXE — the new kernel |
MME |
Multimedia Extensions |
pal |
Platform Abstraction Layer – X11 drivers (not used, reference only) |
samples |
Various sample programs |
tests |
WIN16 unit tests |
user |
USER.EXE |
utilities |
Utility programs |
win |
WIN.COM — Windows loader |
winkrnl |
Windows kernel, GDI, USER from TWIN project (reference only – current kernel is in kernel/) |
We welcome contributions! You can help by:
- Testing the current alpha and reporting bugs
- Porting more Wine/TWIN functions to the 16‑bit environment
- Implementing missing parts (GDI, drivers, etc.)
- Writing documentation and examples
Please use the issue tracker and submit pull requests to the main repository.
Distributed under the GNU Lesser General Public License v2.1 (LGPL‑2.1). See LICENSE for details.
- osFree Project – parent project for an open‑source OS/2 clone
- osFree Janus Clock – sample app
- WinVer – “About Windows” dialog
- Notepad – text editor clone
- Taskman – task manager clone
Project Repository:
https://github.com/osfree-project/WIN16
Keywords:
Windows 3.0 clone Windows 3.0 implementation Windows 3.0 reimplementation
Open-source Windows 3.0 Win16 KRNL286 KRNL386 16-bit Windows osFree
Windows 3.0 compatibility Run old Windows programs DOS Windows
Windows 3.0 repository
- The TWIN, WINE, ReactOS, and HX-DOS teams for their code bases
- Matt Pietrek, Andrew Schulman, Daniel Norton for their books
- All contributors and testers of the osFree project
Last updated: June 10, 2026