A little invoicing application developed writing only 4 simple Java classes: Customer, Invoice, InvoiceDetail and Product. The source code of this demo is included in OpenXava distribution.
A complete ERP with finance, human resources, payroll, inventory management, sales, work orders, business intelligence, reports, etc. This is a commercial product developed by Sicflex using OpenXava and XavaPro.
This is an example of a mobile web application with OpenXava. You don't needed to write any code to have a mobile user interface, just point your mobile browser to your application. This demo uses XavaPro.