This is a very barebones & hacky demo of using OpenType to mix glyphs from 3 different fonts. It's basically just one file (combine.py). fontname.py is something I just copied in from here to rename the font.

To use it, you can edit run.sh to have the actual fonts you want to mix in it.

it's bring-your-own-fonts.

virtualenv venv
source venv/bin/activate
pip install -r requirements.txt
bash run.sh