DisplayFusion Pro (DFP) is a very capable multi-monitor tool. It has many, many useful features but the one that attracted my attention was the multi-monitor taskbars. they somewhat clicked in my multi-monitor environment, unlike plenty of other multi-monitor tools that i have tried. DFP adds a taksbar on each monitor complete with its own start button, tray clock and display active windows that are relevant to each monitor (this feature is customizable) and as an added bonus DFP handles non-standard windows (such as MS Office, Steam, Winamp, Chrome, etc) pretty well.
for a rundown on other prominent features. btw, DFP is extensively customizable, which is a boon to if you like to tweak your workspace to suit your needs. Another plus point is that the devs are accessible and are quite attentive to the users' suggestions and requests. They also promise a lifetime license
for all purchases, as mentioned here