Yeah, then again most people haven't experienced this and are happy to just enable "track changes" in Word and send the document back and forth, maybe if you're lucky, it's hosted on SharePoint or OneDrive.

OnlyOffice, Nextcloud OPffice, Collabora might all have free offerings to a degree, but you'll end up at the mercy of the companies behind those tools and OnlyOffice comes with Enterprise offering that does also cost money.

Costing money isn't necessarily bad, but it's also hard to beat free & libre.

Since this uses Direct2D, is this Windows-only?

How much of the code was vibe-coded?