Probe is a custom control that allows access to other controls properties at run-time. Probe also will display a dialogue box for modifying other controls properties at run-time. This lets you fiddle with properties that are only available at run-time using an easy interface.
Probe can be used as an easy debugging tool. During beta tests, you can include it with your project. Given a little instruction, beta testers can modify things in the field (and, hopefully, report back).
Probe can also be used in a final product. Its very useful as a diagnostic tool.