Alternatives

JavaScript

• medici (JavaScript) is a ledger store optimized for high loads (does not enforce any chart of accounts conventions).

Python

• pyluca is actively developed and has practical use in mind, coined a term 'headless ledger' (different interface and data structures than abacus).
• ledger.py started about 10 years ago with Python 2, was once a hledger competitor, has good documentation, but last commit in 2018.

Plain text accounting

• Ledger, hledger and beancount are leaders in plain text accounting
• See also gnucash

More information

• Open source ERPs (Odoo, ERPNext) all have accounting functionality.
• double-entry-accounting tag on Github is an extra clue for open source accounting information.