Developer website: Michael Watson
Sandbox... For years, standard POSIX permissions did a good job of defining access to our files and folders. But as our needs have become more complex, operating systems have begun implementing access control lists to help handle things. When Apple shipped Mac OS X 10.4, they added a robust granular permissions model. Unfortunately, only Mac OS X Server ships with a GUI for manipulating these permissions.
Enter Sandbox, stage left. What does Sandbox have to offer you? An organized, full-featured GUI for editing Mac OS X's access control lists. A software update system so you never have to come back to this page to check for updates (but you're welcome to anyway). A simple, easy-to-use panel for enabling and disabling ACL functionality.
About that last requirement: Sandbox is a tool for server admins and engineers, and power users—generally intended for those who have at least the fundamentals of ACLs under their belts, and not your typical home user. Apple's File Services Administration documentation is a good place to start to gain an understanding of how the system works.