@MrValentine This project does look interesting. I will take a look and see if they use a custom content management system.
EDIT:
So there is a custom content management system that doesn’t involve the GUI tool. Which is awesome, however there is no download. I have found another community post though where the developer of MonoGame.Forms has roughly explained how you could go about doing what he did.
Link: Building and loading content at runtime?
Thanks a lot for the information!