Formerly OpenERP, this project recently changed its name to Odoo. Newly released, version 8 brings many improvements, including a website builder, e-commerce, online events, Google Calendar sync and alerts, new warehouse management, a new reporting engine, better BI and data analysis, POS (point of sale) hardware integration, a new API, live chat/email marketing, and social media integration. The improvements are ambitious, and there is already a road map for version 9, which promises localization of accounting functions.
Built with Python, Odoo is completely Web-based and backed by a PostgreSQL database. You'll find many add-on modules from Odoo and third parties. Commercial support is available from Odoo directly or from the many partners around the world who also provide implementation services. A fully functional, online version of the system is free for two users, providing a way to evaluate the system with your own data without a time limit or having to do any server installation. You can always upgrade or move the system in-house in the future.
-- Fred Blauer