Quick Sequence Diagram Editor is a tool for creating UML sequence diagrams from textual descriptions of objects and messages that follow a very easy syntax.
It supports actors, constructors, destructors, threads and on-diagram comments that can be used to represent conditions or loops (see example).
Thanks to the FreeHEP Vectorgraphics library, diagrams can be exported in various formats, including PDF, (E)PS, SVG, SWF, EMF, GIF, JPEG.
Quick Sequence Diagram Editor automatically lays out lifelines and messages, there is no need to drag and drop something onto a canvas. So a user should be able to create a nice sequence diagram in a small fraction of the time that one of the grand UML tools would consume.
The aim of the tool is to save you from lots of the stupid work that WYSIWYG applications require, by trading off not too much flexibility. It beats these applications by far when it comes to insert or remove objects and messages. This can be done by just inserting or removing a line of text, the tool will do all the rest.