A Microsoft file hosting and synchronization service.
Thanks for the advice and screenshot. WebClient service is running, still no luck mapping a network drive or adding a network location. I must be missing some other bit.
Also, when I enter the full path to a shared folder using the d.docs.live.net notation in the address bar of the browser, it is now throwing an authentication error at me. A few days ago this was still working.
I wonder if all of this is due to an account and/or content migration behind the scenes, and it's supposed to sort itself out once all our accounts and related OneDrive contents are on the same platform. The reason why I'm guessing this is that I have seen messages like "account migrated" popping up briefly when opening shared folders in the web browser, before getting redirected.