Plugins are special Perl Scripts that interact directly with Understand, they come in two flavors, Graphs and Interactive Reports. They can reference the entire Project, or a specific entitiy, depending on what the author intended. They can be as simple or complex as your imagination, for example the Control Flow Graph that ships with Understand is actually a Plugin.
Be aware that often generating graphs for large projects can be very resource intensive, and in some cases the system can be non-responsive for a long period of time while the graphs are generated.
To install a plugin, simply drag the .upl file into the Understand GUI. You will be asked if you want to install the plugin or edit it. For plugins to appear in the top level menu, Understand may need to be restarted.
Download these graphs by right clicking and selecting "Save As". After installation project level graphs can be run by selecting Graphs->Project Graphs -> [Plugin Name]. Entity Specific graphs can be run by selecting the entity and then Graphs -> Graphs for [Entity Name] -> [Plugin Name].
Project Invocation: This graph creates the call trees for all functions/methods in the project. It is very large, looks like spaghetti, and can be very slow. Use at your own risk.
Variable Tracker: Call tree for how a variable is used. This script works with C/C++.
Download these reports by right clicking and selecting "Save As". After installation project level reports can be run by selecting Reports->Project Interactive Reports -> [Plugin Name]. Entity Specific reports can be run by right clicking on the entity and selecting Interactive Reports -> [Plugin Name].
IReport Template: A small script that shows how to excercise all of the IReport functionality. A very useful starting place for making your own reports.
High Complexity Report: Gives a list of the most complex functions in your project.
Change Impact Report: See what impact changing a particular entity will have on the codebase.
Variable Initialization: Reports where variables in a function are initialized.
Struct Report: Show structures and where they are used.
Variable Tracker: Track everything that modifies a variable, including when that variable is passed as a parameter to another function.
Duplicate Code Finder: Find lines of code that have been duplicated across your code base.
Batch Graph Generator: Generate a chosen graph for all entities in the project, for example all of the call trees or all of the control flow graphs.