There are 2 repositories under atari800 topic.
Millfork: a middle-level programming language targeting 6502- and Z80-based microcomputers and home consoles
Mad Pascal Compiler for 6502 (Atari XE/XL, C64, C4Plus, Neo6502)
Various reverse engineered source code
Ghidra Loaders and FileSystems for retrocomputing platforms
ATASCII screen editor for Atari 8 bits
Atari 8 bit Text Window and FujiNet Library in C (CC65)
This is a mashup between BlocklyVN32X and 8Bit-Unity. It allows you to make Visual Novels for classic 8bit computers and consoles, using a visual scripting language.
Psychedelia/Colourspace by Jeff Minter
Atari Inform Interpreter
SXEGS Cartridge Gerber files and STL models for ATARI 65XE/130XE/800XE/800XL
RetroLoad.com is a web application for converting tape archive files of historical computers into sound.
Port of the famous Sokoban for Atari 800XL with over then 4400 levels on single DD disk.
The most complete collection of Atari computer and console emulators in a single scoop bucket
Code that runs the Atari 8-bit Twitter bot at https://twitter.com/Atari8BitBot
Firmware for ESP8266 to emulated D: and R: for PLATOTerm64 on Atari 8-bit
A small font originally designed for an Atari 800 terminal emulator.
Programs and code snippets for APX Extended Fig-Forth
Attack of the Mutant Camels (1983) by Jeff Minter
2020: Atari 800 emulation using a Teensy 4.0, 3.6 or 4.1 with a standard USB keyboard for input. This is a simplified expansion of Jean-Marc Harvengt's Multi CompUter Machine Emulator M.CU.M.E
Scramble-like game on Atari 800 XL in Action! programming language.
A River Raid game written in Python
A clone of Arkanoid for Atari XL/XE written in CC65
Atari 8-bit Rom Image File Explorer based upon ATR Image Explorer
Atari 8 bit Text Window Library in Pascal (Mad-Pascal)
Source code for RAMbrandt, a graphics program for Atari 8-bit written in FORTH by Bard Ermentrout
A serial terminal program, written in 6502 assembly, for the atari 400/800 to suit my needs for amateur radio.
Download script for Atari 8-Bit Games (Homesoft) at http://www.mushca.com/f/atari/index.php