Jannis is an old and quite unfinished tool for simulating feed forward neural networks. I wrote Jannis back in 2005 while doing a research project for my Diploma thesis in the field of special needs education. It does what I needed it to do. I always planned to continue it, but - by the very nature of this - my time as a university student ended and I never got around to do it.
Now, there are probably better tools out there (e.g. Fann), but it still might be useful.
GPLv2 or later
Jannis lacks a user interface, so you best generate some documentation from the source code (or look at the source, itself) and write some main class that instantiates your neural network.
In short: you need to do some programming in Java in order to use this.
I used some wrappers and little helpers of my Webdings Tools package. You need those in your Java classpath for Jannis to work.