Doesn't Apple literally have a sync solution on this platform, likely using these same APIs? FSEvents powers a lot of core functionality on macOS so it's surprising to hear it just doesn't meet Dropboxes needs.

It's cool they are moving into the kernel soon anyway, just install their kext...

Is Apple's sync reliable though? There was an episode of MacBreak Weekly last week where both Adam Engst & Andy Ihnatko urged people not to enable the new Sierra sync system, and talked about instances of data loss caused by Apple's various sync features. The segment begins here:

https://www.youtube.com/watch?v=IgE1c-YTEpE&t=65m02s

I thought it was common knowledge that Apple's own sync (nevermind the APIs they provide to third parties) was terribly unreliable. Even long-time Mac developers like Panic & Omni developed their own sync services because the Apple ones were so unreliable.

That and what I take to be the iCloud / System Indexing daemon's (like `mdfind`) kill my battery life. The other's reports of poor Dropbox performance baffles me a bit as it never seems to give me issues, but iCloud/Google Drive both have both had big performance penalties on 3 various macs I've tried them on.

That's also my experience - I tried using OneDrive & Bitcasa at various times, and found they used far more battery than Dropbox ever did. I'd consider switching from Dropbox, but the competitors seem inferior to me (and Dropbox has more universal support).

I can't fathom why you think them being a kext is a good thing. I refuse to use anything anymore that needs that, every app that needs that inevitably is a source of something breaking in OS X

Was complete sarcasm

What do they need different from what time machine uses?

Time Machine needs to be able to ask which files changed when it is preparing to backup. Dropbox needs to be notified when a file changes so it can sync.