UML

Online Editors

 * http://yuml.me/
 * https://creately.com/app/#
 * http://www.websequencediagrams.com/
 * http://gskinner.com/gmodeler/launch.html http://gskinner.com/gmodeler/app/run.html
 * https://www.cacoo.com/
 * http://news.ycombinator.com/item?id=594682
 * http://plantuml.sourceforge.net/demojavascript.html
 * http://plantuml.sourceforge.net/running.html
 * http://www.plantuml.com/

IDEs

 * http://www.codeproject.com/KB/smart/plantumleditor.aspx

Drawing

 * http://www.dabbleboard.com/draw

Theory

 * http://www.google.com/search?client=safari&rls=en&q=class+diagram+examples&ie=UTF-8&oe=UTF-8
 * http://www.coderanch.com/how-to/java/AssociationVsAggregationVsComposition
 * http://www.coderanch.com/t/522414/java/java/Association-Vs-Aggregation-Vs-Composition
 * http://geekexplains.blogspot.com/2008/07/composition-vs-aggregation-whats.html
 * http://www.sparxsystems.com/resources/tutorial/uml_tutorial2.html
 * http://atlas.kennesaw.edu/~dbraun/csis4650/A&D/UML_tutorial/class.htm
 * http://www.kuwata-lab.com/erubis/erubisj-users-guide.03.html
 * http://www.uml-diagrams.org/class-diagrams-examples.html