it's also worth checking out http://www.websequencediagrams.com/ http://www.websequencediagrams.com/ i've found it very useful in the past. offers more featur

it's also worth checking out http://www.websequencediagrams.com/ http://www.websequencediagrams.com/ i've found it very useful in the past. offers more features, which was crucial (grouping, notes). the theming is also nice.