ISO Modeling Tool

[LoveToProgrm805]

I am about to start on another project, using the wxWindows API (so that I could use this program on other platforms), but want to try another modeling tool from what I've been using (post-it notes).
Looking for suggestions for a free program that will simulate CRC cards, or UML diagrams, and that lets you manuever objects and connections between them easily.

thanks
Steve