SandboxMirror is a tool for reverse engineering Apple's sandbox on Mac OS X (aka macOS), which is closed-source and almost entirely undocumented. Its internal workings are interesting in themselves. And a better understanding of them should be useful for application developers on OS X -- for example by making it easier to learn how to configure the sandbox intelligently.
SandboxMirror runs on OS X 10.9 (Mavericks) through macOS 10.12 (Sierra).
Steven Michaud, 9/2016