Sequence diagram / Discrete graph tool

Graph tool:
1. GraphViz:
    a. Tutorial: http://graphs.grevian.org/documentation
    b. On-line tool: http://graphs.grevian.org/graph


Sequence diagram tool:
1. PC based:
    a. Mscgen
    b.http://simplecestlavie.blogspot.tw/2012/05/uml-quick-sequence-diagram-editor.html
2. On-line tool:
    a. https://www.websequencediagrams.com/
    b. http://yuml.me/diagram/scruffy/activity/draw
    c. https://grapholite.com/Designer (Many)
    d. https://www.draw.io/# (Many)
    e. https://creately.com (Many)
    f. http://bramp.github.io/js-sequence-diagrams/



Documentation system for source code by graph / sequential diagram:
1. Doxygen
    a. Tutorial:
        * http://www.ibm.com/developerworks/aix/library/au-learningdoxygen/
        * http://www.stack.nl/~dimitri/doxygen/doxygen_intro_cn.html