Paint.NET is free image and photo editing software for computers that run Windows. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.
Perian enables QuickTime application support for additional media types. All major formats supported.
Quicksilver is a unified, extensible interface for working with applications, contacts, music, and other data.
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.
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.
VLC media player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, …) as well as DVDs, VCDs, and various streaming protocols.
Xee is a lightweight, fast and convenient image viewer and browser. It is designed to be a serious tool for image viewing and management, with a sleek and powerful interface.