Michael E. Cohen, at TidBITS:

Dropbox has begun notifying users of its service to inform them that as of 16 January 2018 it will automatically sign out any computers running certain older operating systems. The Mac systems include those running OS X 10.6 Snow Leopard through 10.8 Mountain Lion; Windows Vista systems will also lose desktop support on that date. Not that it matters much, but you won’t be able to download or install the Dropbox desktop app on those systems after 3 November 2017.

Although the vast majority of Mac users have updated their Macs to more-recent versions of OS X and macOS, some continue to run older versions. Many tend to be folk who, like me, have kept a Snow Leopard system operating in order to run PowerPC-based applications; Snow Leopard was the last Mac OS that supported Rosetta, the PowerPC emulator that enabled Intel-based Macs to run such apps.

Then there are folks who, while having a more up-to-date desktop Mac, perhaps keep using an older laptop that’s still working great and can take the occasional rough handling when out and about. Or vice-versa, their older desktop Mac is still useful, but their preferred machine to keep updated is the laptop. These people may need Dropbox to keep in sync two or more Macs of very different vintages. Then there are people like me, who still put even older Macs to good use, and would like to keep relying on services like Dropbox for basic syncing and file exchange. As time passes, however, Dropbox doesn’t seem to be a suitable solution for such needs.

If you’re among these people, my suggestion is to switch to Box. Maybe their pricing plans are nothing to write home about, but for me Box’s killer feature is its WebDAV support. As I’ve reported on my System Folder blog, this means you can connect to your Box storage ‘drive’ even with very old versions of Mac OS X (WebDAV’s support is built into Mac OS X since version 10.0); if you use a WebDAV client like Goliath, you can connect to Box even under Mac OS 9 and earlier (down to Mac OS 8.1!). Read my afore-linked System Folder article for more information.