Same here.
I've tried deleting old stuff, updating applications, removing extensions and startup items, disabling WebGL, not using Safari at all, not using certain applications, unmounting NAS drives (Synology, AFP and SMB), tried Safe Mode etc. The ONLY application other than Finder that I think has been running when it froze is iTunes (listening to music constantly). I've had it freeze previewing jpgs in the finder. It started with El Capitan but has escalated to a near unusable computer with Sierra. Beachball that almost instantly freezes in place, requiring a hard restart.
Some of the time iTunes dies first (the music stops playing just before the beachball), other times everything completely freezes but iTunes keeps playing only to stop when the song has reached the end.
Uninstalled the Logitech driver and things looked promising, but just had a new freeze. iMac 21,5", late 2013, 3,1 GHz, 16 GB RAM, MS Natural Keyboard 4000, Logitech MX Master (recently switched keyboard and mouse, but had freezes with the old MS Keyboard and the old Logitech). Again, started with El Capitan, nothing before that.
Seriously, this is getting way beyond disastrous.