After seeing Synergy's spot on the EVGA iCX video released today, I ventured out to find a free alternative since I'm very low on money atm. I found Mouse without Borders, which works flawlessly between my desktop & Surface pro. I know this has been posted on the forum in the past, but I bet there are many people that don't know this software exists.
Link: https://www.microsoft.com/en-us/download/details.aspx?id=35460
But of course if you need to go between different OS' and you aren't cheap like me: http://symless.com/synergy/linus