Ghoelian

Huh you’re right, seems they even publish specs of their own extensions to the format.

They still restrict what you can do with it and how you can share it though, so technically still proprietary.

Collabora office is based on LibreOffice. I think they mostly just tweak the UI, functionally it’s pretty much LibreOffice.

OnlyOffice tries to be very similar to Microsoft Office I think, similar to Collabora, but they also use Microsoft’s proprietary file format (which I’m not sure collabora does, LibreOffice does not by default)

OnlyOffice uses the proprietary Microsoft file formats, so they were already not an option for me.