v2.6 [May 28, 2013]
Your first script - A guide for total newbies.
Getting started - An introductory guide for getting started with AviSynth.
Filter introduction - An introductory guide to most common AviSynth filters.
Script examples - Assorted examples for putting everything together in the real world.
Some guides explaining the basic possibilities of AviSynth:
Analog Capture guide. The AviSynth part of the capture guide is about what filters can be used to enhance the quality of the capture. It discusses things like deinterlacing, denoising, cropping and resizing and color adjustment. Which makes it really useful to learn about some of the capabilities of AviSynth in a schematic way.
Introduction AviSynth from AnimeMusicVideos.org. A basic guide about deinterlacing, resizing and some other basic stuff.
Introduction basic AviSynth filters from AnimeMusicVideos.org. A basic guide about smoothers, rainbow removal, sharpeners, color adjustment and some other basic stuff.
Troubleshooting your scripts and configuration.
Filters, external plugins, script functions and utilities
Internal filters - The official list and descriptions of included filters, organized by category.
External filters - Documentation of custom script functions and AviSynth v2.5x plugins.
External plugins (old) - Documentation of AviSynth v1.0x/v2.0x plugins (older plugins, some of them are still in general use).
AviSynth plugin collection organized by WarpEnterprises.
Shared functions - Commonly used script functions.
Utilities - A list of GUIs, command-line, batch and other AviSynth related utilities.