Concordion is an open source tool for writing automated acceptance tests in Java. There are also versions for .NET, Python, and Ruby.

Web Site:
License and Pricing: Open Source, Apache License, v2.0

* Why I prefer Concordion to FitNesse
* Writing Stupid Specifications with Concordion
* Concordion vs. Cucumber and Java based Acceptance Testing
* ATDD Acceptance Testing using Concordion
* Automated Acceptance Tests and Requirements Traceability