[atoav]

Horizon probaly has the most flexible and modular library concept there I ever saw. You can reuse things, inherit from things etc.

This is a good summery (with a nice graphic of the structure of an example part): https://horizon-eda.readthedocs.io/en/latest/pool-why.html

[IshKebab]

Wow... documentation?! This looks so much better than Kicad.