Processing is an open source programming language and environment for people who want to create images, animations, and interactions. Initially developed to serve as a software sketchbook and to teach fundamentals of computer programming within a visual context, Processing also has evolved into a tool for generating finished professional work. Today, there are tens of thousands of students, artists, designers, researchers, and hobbyists who use Processing for learning, prototyping, and production.
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file.
VoodooPad is a place to write down your notes and thoughts. Ideas, images, lists, passwords, your mom's apple pie recipe. Include anything you need to keep track of and organize, and VoodooPad will grow with you without getting in the way. Drag and drop folders, PDFs, applications, or URLs into VoodooPad, and they will link up just like on the web. And with powerful search, nothing will be lost or out of reach.
Seashore is an open source image editor for Mac OS X's Cocoa framework. It features gradients, textures and anti-aliasing for both text and brush strokes. It supports multiple layers and alpha channel editing. It is based around the GIMP's technology and uses the same native file format.