If animal companions are like dogs, then familiars are like cats. Less useful but arguably more intelligent!

https://2e.aonprd.com/Familiars.aspx
https://2e.aonprd.com/Familiars.aspx?...

A few sources of familiar related feats I missed, these require an archetype and that you bring your own familiar.

https://2e.aonprd.com/Feats.aspx?ID=3468
https://2e.aonprd.com/Feats.aspx?ID=4342

These are a few feats I left out, only partly by accident as the familiar is a part of these feats but they aren't the focus.

https://2e.aonprd.com/Feats.aspx?ID=1569
https://2e.aonprd.com/Feats.aspx?ID=4192