I know Apache makes one the url is http://java.apache.org It didnt seem very easy to use to me though, so I never tried it. It ia called Apache JMeter 1.5.1 The 100% pure, swing enabled, Java URL profiler/analyzer to test your server performance, your servlet performance, to stress your servlets with heavy multi-threading concurrent requests and much more... [This message has been edited by Randall Twede (edited March 05, 2001).]
Apache JMeter is the only one I have used, but I keep meaning to write my own. The problem I find with JMeter is that it doesn't seem to give me any useful information. It's very pretty with it's dynamic graphs and so on, but I want hard statistics about throughput, latency and failure modes. If we all keep lookimg we may yet find something useful. I can't believe there is nothing sensible out there.
We are looking at tools for performance testing right now and one which looks really cool (and maybe useful) is the Rational software called "TestManager". It lets you look at system calls, and transaction information and lets you slice it in a lot of different ways.