gnuCash is available for all main platforms, Linux/Unix, MacOS (FreeBSD anyway), and Windows.
You can download gnuCash free from here.
It does seem to be fairly full featured and somewhat straight forward, but like so many programs it is missing a few key features or things don't work quite right.
It doesn't support importation of CSV files, which is a big minus. And the developers rather than wanting to add support have just dec........