License
FullStacked is licensed under MIT, but the Editor is under GPL-3.
Which means:
You can build projects with FullStacked as a dependency and redistribute that said project the way you want. (MIT)
If you use any part of the FullStacked Editor, you need to keep the same GPL-3 license, which forces you to open-source the code. (GPL-3)
It is made this way since the main FullStacked packaged app is essentially FullStacked Editor, but that does not limit you to build freely with it.