ATOM is a general environment for agent-based simulations of stock markets. It is platform independent and fully flexible. ATOM allows distributed simulations with many computers interacting through a network as well as local and fast simulations. It can also allow experiments mixing human beings and artificial traders.
I have initiated, with Rémi Bachelet, this project : jESS-X (for java Experimental and Simuated Stock Exchange), an open-source software for experimental finance : do not hesitate to download it, to use it, and to give us your feedback