The Atari 5200 was basically an Atari 400 home computer made into a gaming console to compete with the Intellivision and ColecoVision.

It was meant as an upgrade to the incredibly popular Atari 2600, but it was not backwards compatible with the huge library of 2600 games until a little over a year after release. Not even a year after that, Atari was already advertising the Atari 7800... So, in reality, Atari was also very much competing against itself, discarding the 5200 as a bit of a failure.

Unreleased prototypes and these extras:

"5200 Menu," "Asteroids (Tech Demo)," "Atari PAM Diagnostics (Rev 2.3)," "Atari PAM Final System Test (Rev 1.02)," "Atari PAM: Pete's Test," and "Yellow Sub."

Items removed:
Non-working dumps, duplicates, prototypes of games that eventually saw a release, and modern homebrew games.