The books never actually define exactly what a "free hand" is, and I would like it if someone could make a list of things that makes a hand not free.
Only things that appear in the core rulebook - and where in the rulebook it says that it makes your hand un-free;
I will start -> Holding a weapon. page 140 most of the way down the page "its relative encumbrance (light, one-handed, two-handed)"