jBilling is a web-based enterprise billing system.
jBilling is a web-based enterprise billing and rating system. It manages your subscribers with automatic invoicing (email and PDF) and payment processing (credit cards, checks, direct deposit). Robust, well documented and easy to use!
Evaristo is an ERP solution written in Java (2 tier), though only avaialable in Portuguese, since version 4 is fully internationalizable. It requires a PostgreSQL database in order to store the data.