YaBS is enterprise resource planning software that manages products and contacts as basic data, generates offers, orders, invoices, and reminders from it, and includes basic book keeping. It writes PDF or ODF (OpenOffice format) documents, and is a multiuser system. It is the successor of MP Invoicing. It can use any JDBC compliant database as a backend, and works in heterogenous networks, allowing fine grained security settings. It can also be extended with modules.
Konik provides an easy way to create, read, and validate ZUGFeRD invoices. It features an easy and understandable API, extensive documentation with examples, logical invoice validation with JSR303, validation of invoices against ZUGFeRD profiles, validation of invoices against specific country invoice regulations, easy invoice appending or extracting in and from PDFs, and multiple PDF Carriages from different vendors.