This is a very informative thread:

Especially since LogMeIn is eliminating Cubby and not replacing its Direct Sync capabilities elsewhere in their product line I am looking at GoodSync. In my personal searches, I believe GoodSync (with GoodSync Connect) will give me that same Cubby capability, though it is a bit more complex to set up since it has a lot more features and settings.

Regarding the issue of temporary file names for Excel, since they are not hidden, the synching software may detect and start copying them. If they are large enough, the synch process will have them locked while Excel is trying to rename them, causing a few surprises. As I recall, with Cubby I set up a cubbyignore file (similar to gitignore) to specifically avoid copying these files without an extension (which was good for the folder I needed it for, but may be too general for some folders).

For GoodSync, I am wondering if someone knows the product well enough to suggest how to best avoid this problem. I was thinking that setting a delay of 30 seconds (GoodSync recommends 2 minutes) would be enough time for the file to disappear. The temporary Excel file name is simply 8 characters without an extension, so I am not sure how to best specify an exclusion that won't cause me problems later if I forget and accidentally save something with that pattern.