The Atari 2600 (originally known as the Atari VCS) is a console created by Atari. While that it wasn't the first console or even the first console to have cartridges, it was the first popular console especially in the US. For some people, it was their first time playing games and even received various arcade ports. It was the console that Activision got its break into game development and the first 3rd party developer. Sadly because of poor quality control with various companies making games including food companies and rushed high profile games such as Pac-Man and E.T.: The Extra-Terrestrial, it caused the North American Video Game Crash. Atari had to bury millions of cartridges and something that they didn't really recover from.
Still it has a fanbase to this day who make homebrew games and hacks for the console.
Stella is one of the oldest emulators that still gets updated today and the go to choice for the console. While it isn't perfect to the Atari 2600 considering its system limitations (no video frame buffer so everything had to be done by sending beams to the television), it is extremely close and supports the various controllers that were made for the system such as Paddle Controllers. It also includes an extensive debugger.