The dream of an open source replacement for Windows is still alive after 17 years of development. ReactOS, an operating built from scratch to be binary-compatible with Windows programs and drivers, is nearing its 0.4 release — you can download the release candidate right now.

There are plenty of free, open source operating systems on the market, including hundreds of Linux distributions. ReactOS has always been unique because of its goal –full compatibility with Windows software. In theory this could be revolutionary, but in practice rebuilding Windows from scratch isn’t simple.

For evidence of this you need only look at the list of programs tested on ReactOS 0.4. It notes the Windows versions of many open-source stalwarts, including Firefox and Libre Office, are already up and running. So are a few prominent Windows-only programs, ike WinRAR.

But that’s not to say everything is working. Diablo II, for example, is a game released in 2000 that apparently “installs fine” but “doesn’t run past character selection.” Videos show web-based software, like GOG’s online store, fail to work to varying degrees.

ReactOS isn’t ready to be your primary operating system. And it doesn’t claim to be. The project’s homepage claims it’s only “recommended only for evaluation and testing purposes. Users have tested it, uploading videos of programs they’ve managed to make work (and some they haven’t).

It might seem quixotic, but the ReactOS team keep pushing themselves to build a free version of Windows almost from scratch. Even if they never achieve full compatability with all current Windows app, which is a fast-moving target, ReactOS could wind up being useful in ways that are hard to predict. As older apps break on newer versions of Windows, for example, ReactOS could become the go-to system for running them.

The 0.4.0 release aims to improve compatibility with USB devices, simplify connecting to WiFi networks and improve sound support; a final release date is not available.