Ask HN: What's the best free, simple tool for tracking my money?

I don't know if it's "the best", but Every Dollar from Dave Ramsey is pretty good. Don't know if it will track overall net worth, though.

Spreadsheets

Have a look at Pro Expense which can be downloaded from the F-Droid store.

Gnucash would be an good idea if you want to use the double entry system.

Beancount