CodeRunner
A simple programmer's editor with a tightly-integrated console. It's excellent for rapidly prototyping code with its super fast edit-run-edit -run-save workflow, and its Cocoa integration gives it a real edge over the command line. It has syntax highlighting and code completion for many languages, including AppleScript, C, C++, Java, JavaScript (Node.js), Lua, Objective-C, Perl, PHP, Python, Ruby and Shell, but you easily add the ability to run any language you like. For the person who's always writing a bit of code here and there to do little things that would take too long or be too tedious with Finder etc. or for developers looking to prototype fairly simple code, CodeRunner will be a great help.
