That is one of the reasons I like Stardocks Multiplicity. I haven't tried Synergy, but I'll check them out.
Multiplicity Features
Features
Multiplicity has hundreds of different features for enabling users to customize the look and feel of Windows.
For this guide, we'll stick to the primary features:
●Clip and Paste - Share your clipboard contents among your master and slave computers, including images!
●File and Directory Copying - Easily move files, or entire directories between computers! (Pro Version)
●Hotkey Support - Multiplicity supports fast switching to the connected computers via configurable hotkeys and mouse buttons!
●Fade/Darken Indicator - Multiplicity can fade or darken the non-focus computers, to further enhance navigation speed.
●Onscreen Display - Multiplicity can be configured to display an onscreen indicator of your current location.
●Locking - Support for locking your mouse to a specific desktop (configurable).
●Security - Full password protection, and domain control internally.
●Threshold Option - Full support for threshold control of mouse movement between machines.
●Alternative Control Methods - Multiplicity supports various control methods, such as Jog Dials, and Spatial Controllers!
Fairly priced too.