Apache JMeter

I've been using JMeter for the last couple of years now and it is the best option you have for load testing web application, no matter on which platform it runs on.

Feel free to read my post on JMeter: "Why Apache JMeter is better than HP Load Runner?" at:
http://shmuels.blogspot.com/2012/01/why-apache-jmeter-is-better-than-hp.html

Good luck,
Shmuel Krakower.

I have used this program to test the cluster of IBM Websphere Portal. My experience you can obtain here:

http://nike.homeunix.com/jmeter-and-websphere-portal/