Axure is a powerful program which is used by the major companies for wiretapping and prototyping. It is available for a free-trial.
Some of the most interesting features are:
- Very dynamic content which gives a variety to the users and makes the application friendly.
- The web application has conditional flow and does not take any action without password confirmation.
- Animations can be done without coding.
- Math functions and other data can be visually represented.
- Easy to share with other people.
- The drag-and-drop element makes documentation very easy.