> Free but not Open Source? Did I miss that?

The miniscript language itself is MIT License:

https://github.com/JoeStrout/miniscript

The Minimicro code doesn't seem to have any license in the repository or code:

https://github.com/JoeStrout/minimicro-sysdisk

Mini Micro seems to be built on Unity. The MiniScript portion of it is open source https://github.com/JoeStrout/miniscript but the version packaged for use by Unity costs some money. I can't tell if the people behind MiniScript are the same people behind the Mini Micro.