Best sync software in my view. The only downside is that there is no good iOS app. I think the developers made the right decision focusing the software on peer to peer sync (i.e., not expanding to nearby “cloud features”: backup, photos, videos, office, etc).
"The only downside is that there is no good iOS app." That's a dealbreaker for iOS folks, though. I hate the mission creep Dropbox has embraced, and would definitely consider something else, but I need access to my stuff on Windows, MacOS, and iOS. Anything that doesn't hit all three notes isn't a contender.
I take a photo with with my phone and it's synced to my Linux desktop in 1-2 seconds.