It’s kind of crazy how an addon for Office 97 still works in the latest version of Office over 20 years later. That’s an eternity in the tech world.
The underlying technology is called DirectMusic, and it’s very weird that DirectX had a component for algorithmic music generation. I don’t remember any programs using it (and I don’t remember this PowerPoint plugin), but I remember some SDK (DirectX SDK maybe) or maybe MSDN had examples of using its API, so this technology wasn’t seem too obscure.
This article, which is listed in Wikipedia page for DirectMusic, has screenshots of DirectMusic Producer, which look rad.
I decided to follow through on the reversing aspect. The library is trivially wrappable from C# was it was VBA. Lots of dumb fun things to do with this.