You can use the UVPackmaster SDK Standard edition for free any purpose – non-profit as well as commercial.
The SDK provides a C++ shared library for Windows 64 bit (a Linux version will be released very soon) which you can link with your own application through a well-defined interface.
Download the SDK from gumroad: UVPackmaster 2 SDK STANDARD.
To learn more about the SDK interface and see a sample application code read the documentation.