OST File Recovery, Repair Orphaned Offline Storage Files, Recover Corrupted Data
This is a fairly costly tool for recovering from a number of Outlook/Exchange synchronization disasters. I think it was derived from ost2pst.exe. The latter can be downloaded from several sites, though I wonder if the distribution is legal.
It will, among other things, convert an "orphaned" OST file into a useable PST file.