The ReactOS project is putting out a point-release for the first time in a few years, and this insanely optimistic effort is making progress.
The fact that you can install drivers meant for Windows is on its own absolutely remarkable
ReactOS version 0.4.15 is the first to be given a number in quite a few years. That doesn't mean that work stopped since version 0.4.14 back in December 2021. Development has been continuous for all this time. For all Reg FOSS desk's skepticism about ZeroVer, though, you should take the project's not-yet-halfway-to-one number seriously. We are really impressed with what's here.
This version was split off from the code's master branch about six months ago, and work there continues. So this version is a snapshot of how far the project has got in the last few years. It has improvements in plug'n'play support, sound, memory management, handling problems in the Registry, in its security subsystem, in the "shell" – which in Windows terms means the graphical desktop – and in the bundled accessories.
ReactOS 0.4.15 running Firefox 52 showing Register stories about itself.
ReactOS 0.4.15 can run Firefox 52 happily – just as PaleMoon users prefer – click to enlarge
The Register has looked at the progress of ReactOS several times over the years: at version 0.4.9 in 2018, then version 0.4.11 in 2019, then 0.4.13 in 2020, and most recently at the previous version to this one, 0.4.14 in 2022. It is a remarkably audacious project: it's an attempt to reverse-engineer an OS that's so compatible with Microsoft Windows NT that it's not just possible to run Windows applications – because WINE can do that rather well nowadays – but also run Windows drivers. And it does seem to be getting there: for instance, we were able to install the VirtualBox Guest Additions, and thereafter ReactOS said it was using a VirtualBox display adaptor. We couldn't choose high resolutions or anything, but it did work, in what it says is 32-bit color.
For now, what you get is an x86-32 OS which, even when we gave it two virtual CPU cores and told it to install for an ACPI SMP computer, still seemed to be running on just one. The desktop watermark says that it reports itself to apps as Windows NT 5.2 Build 3790: Service Pack 3. That equates to Windows XP Pro x64 edition, or alternatively, to Windows Server 2003, which is what XP for x86-64 was based upon.
As The Reg reported way back in 2004, XP 64 trailed the x86-32 version by several years. The Reg FOSS desk installed a fresh copy of XP 64 just two years ago and we are almost ashamed to admit that we really enjoyed the experience. Compared to modern Windows, it's sleek, elegant, and fast. We also experimentally installed Windows Server 2003 Enterprise recently, because it (along with the Datacenter edition) are the only 32-bit flavors of Windows that can support more than three-and-a-bit gigabytes of RAM. We experimentally tried assigning 8,000 MB of RAM to our ReactOS VM but it still only saw 3.5 GiB.
The fact that you can install drivers meant for Windows is on its own absolutely remarkable, and The Register has reported in the past on a Microsoft kernel engineer's disbelief that it could be achieved without access to original source code. The ReactOS project adamantly maintains the cleanliness of its clean-room reverse engineering, and indeed, nearly 20 years ago it paused development for thorough checks after accusations that some contributors might have seen Microsoft source code.
This vulture switched to Linux (and some Mac OS X on the desktop) full-time back in about 2002, from despair at the bloat of Windows XP. We've never seen any reason to go back, and Windows 11 finally extirpated any remaining nostalgia. For us, ReactOS is an amazing recreation of a sweet spot in the history of Windows NT: the very early boot process is in text mode, like NT 4, but the desktop resembles something from around the time of Windows 2000 – without XP's bolted-on themes – so closely that it's positively eery. It's a pixel-perfect recreation of Windows from about the last time we actually liked using it.
ReactOS has a sort of app store which contains nearly 400 programs that it supports.
ReactOS has a sort of app store which contains nearly 400 programs that it supports. - Click to enlarge
The built-in "WINE Internet Explorer" browser didn't work at all for us, but there's a pre-installed Applications Manager which can fetch and install 358 free apps that ought to work, including some elderly versions of Firefox.
We don't personally have any particular need for Windows at all in 2025, let alone a 32-bit single-core Windows-compatible OS, but the fact that it installs and runs at all is seriously impressive. If you do, you don't own a license, and you don't want to risk pirate copies even of over-twenty-year-old OSes, then this is a remarkable achievement.
We know that we're not alone in preferring older versions of Windows. Some hardcore gamers run Windows 98SE even now, which sounds downright masochistic to us. If ReactOS ever gets to the point where it can run most modern Windows apps successfully, even excluding OS integration, we fear that Microsoft will find some justification to sue the project so far into oblivion that not even a smoking crater remains. Until then, though, it's amazing stuff, and we recommend experimenting with it. ®