ESS™ has several support options based upon your needs:

Source Forge - ESS™ is supported through the expense-ss project. Besides downloading the release package and source code, bug reports and support requests can be created.
Yahoo Open Source Expense User Group - This is a message group for ESS™. Send any questions or make suggestions. ExpenseServices.com personnel monitor the user group hoping to answer your questions and put your suggestions to work
ExpenseServices.com - An ESS™ test/demo site is available, as well as, the most recent documentation to all registered users.
Contractual Support - Support is available at ExpenseServices.com, or by phone, between the hours of 9 AM and 4 PM Pacific time. Prioritized support plans are available. Contact us to find out more.

ESS™ — An open approach