Audacity is free, open source and cross-platform digital audio editor and recording application. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems.
WavePad is a full featured professional audio and music editor for Windows and Mac OS X. It lets you record and edit music, voice and other audio recordings.
GIMP is a free Image Manipulation Program. It is brilliant for photo retouching, image composition and image authoring. It works on many operating systems, in many languages.
Inkscape is an Open Source vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
Movie Maker is installed by default within Windows XP but is an optional download for Windows 7. Movie Maker uses drag and drop to make creating and editing movies easier. There are a number of add-ons and upgrades available through the official website. For Windows users this is probably the easiest way of editing video.
Apple iMovie is the Mac equivalent to Windows Movie Maker. Apple iMovie has many advanced features and add-ons but is only free if it is installed with your Mac system. Standalone versions are available for purchase. This is one of the best options for free video editing on the MAC platform.
Wax is a free video editing software application and is suitable for both home users and professionals. It can be used as a stand-alone application, or as a plug-in to other video editors (Sony Vegas, Pure Motion EditStudio & Adobe Premiere). The software features unlimited video and audio tracks with top-down compositing.
Zwei-Stein is a freeware non-linear, non-destructive video compositing and editing system which offers many advanced features unavailable elsewhere. With Zwei-Stein you can edit up to 256 video, audio and still image clips, each with up to 64 effects chained serially. Cropping, panning and custom effects are easy with automatic key frames.