LedgerSMB is a web-based open source financial accounting and ERP program for small to midsize businesses.   It offers solid AR, AP, and GL handling  (all capable of enforcing separation of duties) as well as fixed asset and inventory tracking.  Free add-ons include capabilities for CSV imports, and budget tracking. By leveraging a completely open source software stack the software itself is highly extensible.  New features can be easily added, and the software can be seemlessly integrated into one's business infrastructure.