JSAP started out as a one-person project, but has since grown thanks to code and idea contributions from its users. I hope the following is a complete list. Please let me know if I'm leaving anyone out.
Contributed the QualifiedSwitch and EnumeratedStringParser classes, plus a few bug fixes.
Suggested the ability to override the use of the ID in automatically-generated usage information.
Suggested the ability to mark command line parameters as mutually-exclusive.
Implemented mutual exclusion and its complement, mutual requirement of parameters.
Pointed out a few bugs in the Ant task and provided solutions (the best kind of bug report there is!)
Provided the FileStringParser class.