From the historic to the latest; if it's Atari it's here.

Large archive of files. Includes word processors, utilities, audio, video, games, emulators and programming utilities.

Freeware/Shareware for Atari: PH Player, Rejoinder, PHEM.

Several ROM files available including Basic.

All the classic games you remember. Extensive list of files. Bin and exe formats.

FTP listing with several downloads available.

Technical documents including pin-outs and protocol specifications. Also includes pictures and some utilities.