ReactOS

1996 → today · Windows

A free, open-source operating system written from scratch to work like Windows.¹ It began in 1996 and is not made by Microsoft.^{2, 4}

▶ Try it Sources

Project started: 1996, as FreeWin95^{2, 3}
Made to run: Windows programs and drivers¹
License: Free and open source¹
Our lesson uses: ReactOS 0.4.16, from August 2026⁵

Why it was made

Around 1996, a group called FreeWin95 set out to build a free copy of Windows 95. They talked and planned, but had nothing to show.³ At the end of 1997, Jason Filby took over and restarted the project with a new target: Windows NT. It was renamed ReactOS, as a reaction to Microsoft's monopoly on home computer operating systems.^{2, 3}

ReactOS 0.4.16 starting from its CD in our virtual PC. The same CD lets you try ReactOS or install it.⁵

What it looks like

ReactOS looks and feels like Windows, and it can run Windows programs and drivers. As of November 2026, not every program works, so the team suggests testing yours first.¹ It has its own versions of familiar Windows tools, from Notepad to the command prompt.⁴

ReactOS desktop with a Notepad window titled '*Untitled - Notepad' holding the typed line 'hello from the os museum'. Desktop icons on the left: My Documents, My Computer, My Network Places, Recycle Bin, Command Prompt, Install ReactOS and Read Me. The taskbar at the bottom shows a Notepad button and the clock. — Notepad in ReactOS, opened with Start, then Run, as in our lesson.

Where it is today

As of November 2026, the newest version is 0.4.16, from August 2026.^{6, 5} It brought a new graphical installer, and one CD now lets you try or install it. For years the team kept strictly to what Windows Server 2003 offered. They have since loosened that rule, but releases are still built to match it.⁵

ReactOS desktop with a space wallpaper showing planet Earth. The Start menu is open with Programs, Documents, Settings, Search, Help and Support, Run and Shut Down. The bottom corner reads 'ReactOS Version 0.4.16-x86'. — The ReactOS 0.4.16 desktop in our virtual PC, with the Start menu open.

Key moments

1996 Around 1996, a group called FreeWin95 sets out to make a free copy of Windows 95.³ ReactOS counts its birthday from the first entry in its code history, in January 1996.²
1998 In February, the project starts again as ReactOS, now aiming at Windows NT.³
2003 ReactOS 0.1.0 comes out on 1 February. It is the first to start from a CD, with a command line but no desktop.²
2016 ReactOS 0.4.0 comes out on 16 February, with a new desktop shell built more like Windows Explorer.²
2026 ReactOS 0.4.16 comes out on 29 August.⁵