AAY stands for "All About Your...". This is a mighty help-system for C64-coders done by Ninja. A (really) lot of documentation has been collected and put to a hyperlinked context. So, with just a few clicks you should be able to find the information you need for developing. Different devices have their own AAY, like the C64 or the 1541 floppy-drive. You can download a version for PC-DOS, HTML or ASCII.