This site has everything, from assembling Atari 8-bit computers based on the 6502 chip, to programming them in BASIC and assembly, to running official and homebrew games on the hardware itself.

Atari BASIC was remarkably easy to program compared to the Commodore's Microsoft BASIC. C64 basic, yes. But the C128 basic was a different beast.

Luckily, there is a Twitter bot out there that can let you experience an old 8-bit Atari without even needing to spin up an emulator. Just tweet your program to the bot, and it outputs the result.