Does anybody know a FOSS zero-based budgeting software? GnuCash or Firefly are great double-entry systems, but for personal budgeting I prefer YNAB or Everypocket styles.
You can simulate various forms of envelope budgeting in Ledger (aka. ledger-cli) and the similar projects like hledger. There are quite a few of blog/forum posts out there that help explain how to do this. If you're specifically looking to emulate YNAB, there are also some posts that deal specifically with this.