!!!OSS Basic A+ ; Copyright (C) 1981 OSS, Inc.
Atari BASIC had been designed to fit in a single 8k cartridge, with an optional second cartridge adding additional capability (the Atari 800 home computer featured two cartridge slots). However, the second cartridge was never produced.
Instead, OSS produced a disk-based product called BASIC A Plus (or BASIC A+), which was compatible with Atari BASIC but corrected several bugs and added quite a few features. Among the notable features were PRINT USING (for formatted output), trace and debug enhancements, direct DOS commands, and explicit support for the Atari computers' exceptional graphics hardware.
Because BASIC A+ had to be purchased, programs developed using its extended features could not be shared with people who did not own the interpreter.
Available on disk only.

* [OSS_BASIC_A_Plus_3.1_Manual-May_1981.pdf] ; size: 1.5 MB
* [OSS_BASIC_A_Plus_3.1_Manual-May_1981-2.pdf] ; size: 13.9 MB
* [OSS_BASIC_A_Plus_Demo_Disk.pdf] ; size: 770 KB

* [Review for OSS BASIC A+ in ANTIC VOL. 2, NO. 2, MAY 1983|http://www.atarimagazines.com/v2n2/productreviews.html]