Feature rich accounting package (specifically designed for oil industry but not limited to) based on php and PostgreSQL. It will closely follow the perl based GPLed sql-ledger package hosted on sourceforge.
It appears that this project has stalled. Take a look at LedgerSMB. Here you will find an ERP system with the same roots and goal; "developing an API, to access all SL data via - from any language/program - without anyone but the API touching the actual data" http://www.ledgersmb.org/