AviSynth is a powerful tool for video creation. This program provides almost unlimited possibilities for editing and video processing. AviSynth works as a frameserver, providing instant video editing without the need to use temporary files.
AviSynth itself does not have a Graphical User Interface (GUI), but is based on a system of scripts that allow for advanced non-linear editing. Although such a solution may seem tedious and uninteresting at first, it is also a great tool for project management in an exact sequence.
Because scripts are text-based, they are easy to read and understand, especially if they are self-documented. The script language is quite simple, but with the help of basic operations you can create powerful and complex filters that will reveal all the features of unique effects.
AviSynth offers almost unlimited video editing possibilities without the need of creating temporary files.