That's an excellent program. I downloaded it per your suggestion, but I really wanted a web based version. Thank you though, I will find many uses for this program as well.

Dot itself is also a command line tool, so it's easy to make documents and presentations with TeX that have text-format diagrams in the dot language. You can also do things like generate call graphs for programs, or parse log files into sequence diagrams by parsing input somehow and generating dot files.