iTerm2 is a terminal emulator for Mac OS X that does amazing things.

Staggeringly powerful macOS desktop automation with Lua

Mac app that shows all open files, directories, sockets, pipes and devices in use by all running processes. Nice GUI for lsof.

A window management application (replacement for Divvy/SizeUp/ShiftIt)

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Quicksilver Project Source

A simple CSV editor for the Mac

A window-based context switcher for the Mac