OpenSCAD models by NascentMaker is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Most projects already include STL files. You can download these directly and 3D print them. Some may require you to split the separated parts into their own objects in your slicer.
These objects require the BOSL library in order to work. It's included as a submodule in this project. Check out the code by running this command:
git clone --recurse-submodules https://github.com/NascentMaker/OpenSCAD-Models.git
Once you have checked out the code you can modify the models directly in OpenSCAD using the customizer or by modifying the code directly.