A Microsoft file hosting and synchronization service.
I can understand why Microsoft and other companies cannot be expected to support older versions of software, in this case OneDrive, ad infinitum. But that does not mean they cannot maintain a webpage of legacy versions for those who, for one reason or another, are unable to update their OS.
I had that trouble with OS Mojave on one of my Macbooks (I have several in several locations and THAT is why it is so useful being able to store files and manuscripts etc I am working on in the cloud on OneDrive.
However, on that Macbook try as I might I could not install any version of OneDrive. I have no idea why. Finally, I upgraded to Catalina, the next OS up and OneDrive installed just fine.
HOWEVER, the whole point of staying with Mojave had been because it was last OS X which supported 32-bit software. So now there are several programs I can no longer use on that machine.