In the Iisu Free license specifications, it is explicitly mentioned that the software runs only on Windows PC. 

Is this also the case with the Premium license? Are other platforms (Linux/Unix, Mac) supported?

Hi Tobias,
The commercial license of iisu indeed supports Linux, in addition to Windows. We have demonstrated our software and hardware technologies last week and this week on Intel set top box at IBC in Amsterdam and IDF in San Francisco
If you would like to discuss specific requirements, please contact sales@softkinetic.com, and one of our account managers will get back to you.
Thanks!
Virgile