Create sequence diagrams with very simple text markup. No dragging around shapes, no manually drawing arrows. Just write out the sequence in text and get the nice looking flowchart.

Source: WebSequenceDiagrams – Draw UML sequence diagrams online in seconds

File this under Very cool but may be too cumbersome to use. WebSequenceDiagrams.com allows you to write out a sequence diagram, and it will take your text and create the diagram.

If you need to create sequence diagrams for students, then check it out!