A class library for managing user configurable options.
With the "opt" library, you can build a model for your options (in XML or Java code) and then use that model to perform various tasks.
You can present the options graphically so a human user can configure them with validation. You can also generate a usage-summary for a command-line appliction.
If the options are for a command-line program, you may want to emit a command-line string that corresponds to the state of those options. You may also want to parse an existing command-line string to assign values to your option objects.