- [Extensibility is core](http://www.openpetra.org/organisation-benefits)
- Ledger-specific access control, three access levels.
- using fixed point arithmetic: System.Decimal data type for all money related variables (changed from Double to Decimal in end of 2010: [commit](https://github.com/openpetra/openpetra/commit/a1717237825a6c8f0d5e032c843241ed918e2344))