Just a comment on the statistics - this is not a vote for which is the best multi-monitor tool, it is weighted by which tool people have experienced.
The win10 multi-desktop feature is really crude, but comes out high in the counting.
You could do more by letting ppl tick boxes as to which they've used & which they liked, and I'm 'sure' it would be easy to get something useful from those statistics ;-> ( - in other words don't ask me how exactly to do that...)
I used to use UltraMon, but for the same reasons as the above commenter was disappointed, I decided to check out DisplayFusion. I felt it did everything I needed it to, and it was cheaper to pay for the "Pro" version versus paying for UltraMon. I really hoped Windows 7 would have adapted the multi-monitor wallpaper manager, as well as some form of taskbar enhancement upon release, but I think we'll have to wait on that. Titlebar buttons are another feature I loved in UltraMon that are in DisplayFusion (for cheaper).
I love Synergy, and would have voted for it if I didn't consider the competition it was up against. Everything else up there was a software for desktop extension (on a single computer), Synergy is kind of in a league of its own, and it's the best thing out there in that league.
I love UltraMon; enough to never to have bothered with any of the others listed, but I'm disappointed lately that there doesn't seem to be any recent updates to improve Win7 support with their Taskbar extension. Would be great to see that Win7 peek-whatsit feature (which I admit I don't actually bother using); but more importantly drag-drop functionality for app re-ordering. These inclusions would at least make it feel as slick an 'essential app' as I've always felt UltraMon was.