Apache JMeter
This is our primary software testing platform. It's java all the way down, provides some fairly good out-of-the-box functionality for verification and performance measurement, and while it has some rough edges, none of them are fatal. Given the active jakarta development community and high level of interest in SOAP services, the future is bright. The JMeter interface for actually building tests is the clear winner, and ease of installation and operation is a plus.
Tsung
Tsung was and is interesting on paper. In practice, however, while it's under active use and development, it lacks decent release engineering and has more rough edges than not. We may revisit Tsung in future for automated testing of the MIT Jabber service.
TestMaker
TestMaker has the look and feel of monolithic IDEs and debugging environments, with a user interface that will feel very comfortable to Microsoft Windows users. Once past some installation issues, it definitely leads in user-friendliness and ease of getting started testing (complete with large, friendly "push to test" buttons), and it has testing-building agents that can pull down a WSDL and build a basic test for you with almost no effort. Beyond the basic level, though, you get some useful libraries and the full power of a high-level language to hand but for the most part you're on your own writing your test scripts in jython. (Alternately, TestMaker can be thought of as a Python IDE with some extra user interface widgets and useful class libraries.) We do currently use TestMaker for some prototyping and test development work, but not as part of the nightly grind. A note on installation: TestMaker gets special mention for being absolutely opaque about undocumented JRE and CLASSPATH requirements, especially as seen in the BEA and IBM JRE packages provided with RHEL; the BEA 1.5 JRE currently seems to be doing the job.
tcpmon (https://tcpmon.dev.java.net/)
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[Adapted from an email report from November 2006.]