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.