OneDriver is a native Linux filesystem for Microsoft OneDrive. The tool mounts OneDrive and then allows you to access it from your file manager and other applications as if the files were on your local hard disk.
Using OneDriver, the files are only downloaded when you open them. This means that if you have a lot of files in your Microsoft OneDrive, you don't have to wait for all of them to be downloaded before using them, and you don't need to use selective sync. Any modifications or new files you create in the OneDrive folder are automatically uploaded to Microsoft OneDrive (and vice versa).