I needed to know which tool do you use to model your system/software? I mean to create sequence diagrams, flow, etc...
I have found Visual Paradigm Community edition...I think I used this one a long time ago at school...
IBM's Rational Software Architect is a great tool. I have used it extensively for sequence diagrams, but I was privileged to have the license as part of my work.
For my private use, StarUML can be a great free tool.