FIXimulator is a Java based sell-side FIX trading application built on the open source QuickFIX/J FIX engine. Its main intended purpose is to be used as a testing tool in writing, building, and analyzing buy side trading applications that use FIX. It requires Java 6 to run and a buy-side FIX application to talk to. If you do not have a buy side application Banzai is available to download from this website if you just want to simply download and try out FIXimulator. Banzai is an open source sample buy side application that comes with the QuickFIX/J FIX engine. The version here has minor adjustments so that all functionality of FIXimulator can be demonstrated.
I wrote FIXimulator as a thesis project. I haven't had a chance to repackage it as an org project but I will get around to doing that eventually. The thesis document can be downloaded from the Downloads section on the left. It contains an introduction to FIX and some other potentially valuable general information. It also contains a User Guide that you will likely find useful.