I have an old i3 PC that I'd like to useas a NAS but I'd prefer to use FOSS instead as realistically I don't know even this is even the solution I want to go with and would rather avoid dropping a lot of money on something I may change.

EDIT: Thanks everyone for the suggestions. I will be bookmarking them all. Probably give TrueNAS a go first since I've heard of it before. (I think from LTT.)