Answer by: Gordon
Aside from the fact that GRT is a very complex application and could only be a very simplified mobile app, the current amount of work is purely enough.
Maybe a simplified webapp could be possible in the future, but as a native program for other OS's there are e.g. technical and licensing problems, platform changes, missing tools, the lack of testing-hardware or whatever. In the most cases, any niche OS has the ability to emulate and start Linux and/or Windows programs, like CrossOver or Parallels for Apple MAC.
Not the initial development/port to a specific OS is the most time consuming, it is the maintenance of the state you archive. E.g. a Linux on ARM port seems to be very easy, because it looks like “just” a compiler switch for the correct CPU, but every OS has its own quirks and problems that need to be solved. At some point, you're just tinkering around with OS-specific problems, or you have to create workarounds for bugs in other people's libraries instead of taking care of the core and the maintenance/development of the important data.
In this regard we choose rather to hold and maintain the quality instead satisfy any user OS wishes!