Java Modelling Tools is a suite for performance evaluation and modelling. Queuing Network models are solved with analytical, asymptotic and simulation methods; workload is characterized using clustering techniques.
My company is small so I've been looking at low cost tools for modelling networks of queues. JMT has proven to be very comprehensive at the same time as being easy to learn to use. I am looking forward to the imminent release of 0.9.0 as it will hopefully address the assembly line reality where sub-assemblies are "consumed" into higher level assemblies. An excellent tool!
I'm using JMT in my PhD project and it is working very well. The discussion forums are very useful and I get lot's of help very quickly. My university team mentioned that they use JMT in their lab and they also recommend it. I recommend this tool.