SynthTest is a somewhat simple application for OS X that allows you to pick a MIDI source, a MusicDevice AudioUnit, and an Effect or MusicEffect AudioUnit to play with. You can open an edit window for both the synth and effect. If they do not have a custom edit GUI, the generic editor view will be used. SynthTest has a reference implementation of preset support for Audio Units. It is primarily intended to be used by Audio Unit developers for testing purposes (the source is available), although it can be great fun to play with all by itself. It is complete enough to be used for live performances.
EOS Image Manager is a pure Cocoa application that enables users to quickly view, thumbnail, rename (add and remove chars, change case), and manage (move, copy, and rename) all of their images from a single, uncluttered interface. With this application users can organize thousands of downloaded images and digital photos in minutes.
X Resource Graph (XRG) is a system monitor that shows graphs for CPU usage, memory usage, battery status, machine temperature, network usage, disk usage, current weather, and stock market data. It is designed to use as little overhead possible while showing a lot of information about the resource usage in a nice interface.
XShelf is an application that enhances Drag and Drop operations in MacOS X by providing a shelf where drag-and-dropped items (such as files, text, or URLs) can be stored for later use. Thus, not only can Drag and Drop operations be "paused", multiple operations can be in flight at once. It is the spiritual heir to the NeXT Shelf.