source 7/16/2017: https://support.balsamiq.com/sales/multiplecomputers/
I Have Two Computers That I Personally Use. Do I Need to Purchase Two Licenses?
The license for Mockups 3 for Desktop is tied to the user, not a particular machine.
And if you have two different operating systems, that is ok too! Mockups 3 for Desktop runs on Windows and Mac via Adobe Air. System requirements can be found on our download page.
Install it on any machine you use regularly, and enjoy!