The long-running Atari fansite AtariAge sells a number of carts that run on classic Atari VCS systems that make it do things you might not expect that system could do. Some of the most impressive of these are remakes of classic arcade games that go far beyond what was possible at the time. A number of these were developed by Champ Games. Here are links to a number of videos showing them off, although sone of the may not currently be in their store:
“Galagon” – Wizard of Wor – Zoo Keeper – Avalanche – Scramble – Super Cobra – Mappy (especially this one!)
A few others, not from Champ Games: Aardvark (Anteater) – Venture Reloaded – Space Rocks (Asteroids) – Star Castle – Pac-Man – Draconian (Bosconian)