Lightweight UML sketching tool - UMLet

For years, I have been searching for a lightweight tool to quickly draw UML diagrams - in order to brainstorm an idea with my team. The traditional tools I have been using for UML were Rational Software Architect, IBM System Architect, Visual Studio 2010, Visio, ArgoUML, etc.

All the above tools are good, but are quite heavy to use and require installation. If you need a robust and quick UML sketching tool, then UMLet will blow your mind :)

I was particularly impressed with the simplicity of the tool. Drawing class diagrams, sequence/activity diagrams, package structures, deployment diagrams are a breeze....And it can run standalone as a JAR file or as an eclipse plugin. Loved the 'geeky' properties editor. U need to use it to appreciate it :)
It does not support code generation, as it was not the design intention of the tool.
Highly recommended for all agile architects!

Activation bar in UML Sequence Diagrams

A lot of folks get confused between the "life-line" concept and "activation bar" concept in Sequence Diagrams.

The vertical lines drawn are called the lifeline of the object. When the object is no longer alive, then we can draw an 'X' at the bottom of the line. So why do we need an activation bar? I have seen a lot of architects choosing not to draw the activation bar to keep the diagrams simple.

The activation bar (a.k.a focus of control) represents the time the object is "active", i.e. doing some processing, computing something, waiting for a response from a sub-routine, etc. So it is possible to model multiple interactions in a single diagram - for e.g. a lifeline can have nultiple activation bars.