Yes, you can use Pianoteq on 3 different devices at the same time, and with different OS… You just have to register your device on Pianoteq’s web page…
You can even decide to un-register one device, and register a new one…
But, once you un-register a device, you cannot register it again…
Or yes, it is still possible, but you would have to write a mail to Modartt explaining why you canceled the registrationn and why you would want to register again…
Also, registering/unregistering, is done by connecting to the web site using the specific device which you want to register… this means that if you have no more access to this specific device (it’s dead, or stolen, or no more connected), un- registering it is not directly possible, and then only a mail to Modartt could solve the problem…
All this also means that, in case Modartt would stop all activities, then you would no more be able to install Pianoteq on any new device…
Long live to open-sources and freewares…
Have a nice day…
Thierry
PS/ Edit… all this is also true for the extra pianos that you might have bought from them…