free Flow chart programs?

I've finally reached a stage in my project where I *need* a flow chart to keep track of the way various parts of the combat system are interacting with each other and to plan out way to make it upgradable for easy add ons of new weapons and game mechanics. Anyone know of some free flow chart programs that lend themselves well to showing logic gates and if>then loops?

I know only that this exists and worked for the 5 minutes I played with it on Linux. There is a Windows version available. Hope it helps: http://www.gnome.org/projects/dia/