With HotkeyNet, you can (for example) put the cursor on a certain location in one WoW, press a hotkey, and HotkeyNet will generate a mouse click in one or more other WoW's at the corresponding locations in their windows but not in the foreground WoW where you positioned the cursor. The WoW's that get clicked can be covered by other windows, and they can be on other PCs.

You can do various things of this sort -- this is just an example.