> It's shocking to me that Microsoft aren't heavily involved with the project considering it's one of the fundamental frameworks for releasing software on Windows.

The history of WiX is that it started internally at Microsoft. IIRC it was a project under the Office organization originally. It's generally considered the first big open source success of Microsoft in spinning a project out to open source community ownership and paved the way for almost every later open source project at Microsoft.

I've got a feeling Microsoft doesn't want to support it anymore because they see it as completely legacy today. WiX is one of the better/cheaper/harder ways to build an old school MSI file. MSI installers are an ancient archive format (the old CAB format) wrapping an ancient and dying DB format (the old JET database engine) and a lot of the complexity of the WiX toolkit is just a reflection of the complex legacy of the old terrible MSI output format. Today Microsoft suggests using MSIX which looks a lot more directly like the better/simpler input to a (well crafted greenfield) WiX project, it's a plain ZIP file with XML metadata.

> IIRC it was a project under the Office organization originally.

I worked in Office in 1999 when I created WiX but it definitely was not an "Office project". It wasn't until I left Office for project in Windows Server that Office adopted the WiX Toolset (to replace their custom system). The interaction with Office was always interesting.

> I've got a feeling Microsoft doesn't want to support it anymore because they see it as completely legacy today.

I think that's probably fair. The problem is that nobody has created an installation technology that is as fully featured as the Windows Installer. There are a lot of warts to the Windows Installer. It was designed to support floppy disks for goodness sake, but they were the last team IMHO that took the installation problem seriously. That's why MSI hasn't been replaced in 25 years.

> WiX toolkit is just a reflection of the complex legacy of the old terrible MSI output format.

Our primary goal with the WiX Toolset was to provide access to the full power of the Windows Installer. Given the adoption by extremely large software projects, I think we've done pretty well toward that goal. We're slowly turning our attention to simplifying the toolset to make it easier to use for simpler projects. But that's only been a focus for the last couple of years, so not a lot has come about, yet. But the Files element is a huge upgrade.

For reference, here is the MSIX Toolset code repository:

https://github.com/microsoft/MSIX-Toolkit