A Microsoft file hosting and synchronization service.
Indeed, OneDrive is the buggiest application I have encountered recently. It is slow as molasses to sync (e.g., on a 1GB/s connection it has been syncing a 1MB file for the last hour), often fails to do so, sometimes creates fake duplicates (where it believes there is multiple simultaneous edits, when there isn't), quits on its own several times per day, and often blocks files. Why can't MS just buy Dropbox and use its tech instead of this crappy in-house development?