Thank you. Picture Link
You may try UMLet. It supports all UML type diagram and you can use activity diagram. Here is sample of activity diagram:
Short about UMLet:
UMLet is a free, open-source UML tool with a simple user interface: draw UML diagrams fast, build sequence and activity diagrams from plain text, export diagrams to eps, pdf, jpg, svg, and clipboard, share diagrams using Eclipse, and create new, custom UML elements. UMLet runs stand-alone or as Eclipse plug-in on Windows, OS X and Linux.