OpenFakt is an open source Java invoicing and billing system using XML definition files for various forms (address book, articles, invoices, stock management). It is language, database and platform independent and aims at small to big companies.
OpenAspect - entire business, one place.
A scalable, secure ERP and CRM system, including Asset management/servicing, Inventory, Logistics, AP, AR, GL, and more.
Front-ends can be 'plugged-in', using PHP, ASP, Java, Delphi, and many more.