Jitter (advanced):

http://www.cycling74.com/products/jitter.html

Jitter is a set of 135 brilliant video, matrix, and 3D graphics objects for the Max graphical programming environment. The Jitter objects extend the functionality of MaxMSP with flexible means to generate and manipulate matrix data -- any data that can be expressed in rows and columns, such as video and still images, 3D geometry, as well as text, spreadsheet data, particle systems, voxels, or audio. Jitter is useful to anyone interested in real-time video processing, custom effects, 2D/3D graphics, audio/visual interaction, data visualization, and analysis.

Since Jitter is built upon the Max/MSP programming environment, the limitations inherent in fixed purpose applications is eliminated. You are able to build the programs you want to use, rather than being forced to work around somone else's idea of how things should be done. This power is not to be underestimated, so please use it wisely.

VVVV (advanced):

http://vvvv.meso.net/tiki-index.php

vvvv is a toolkit for real time video synthesis and physical devices. It is designed to facilitate the handling of large media environments with physical interfaces, real-time motion graphics, audio and video that can interact with many users simultaneously.

vvvv is focussed on the following requirements:

• Runtime graphical programming and easy prototyping
  
• Effortless handling of a multitude of objects (Spreads)
  
• High-Speed, High-Quality, High-Resolution DirectX9.0 based rendering
  
• Sophisticated objects for high level animation and problem solving
  
• Controlling hardware devices
  
• Support for clustering of standard PCs to create seamless multi-projection or multi screen setups
  

Resolume (easier for strict end user live mixing):

http://www.resolume.com/index.php

Resolume is an instrument for live video performances. Completely build to quickly improvise your videos to the music. Play up to three layers of video, with up to six effects. Play video forward, backward, adjust the speed or scratch it by hand. You can freely improvise without ever stopping the video. Resolume is the preferred software of choice for many professional VJ's and video artist in 40 countries worldwide.

http://www.fckeditor.net/default.html

Looks like a powerful HTML text editor similar to Macromedia Contribute except this is free and platform independent.