The Atari 2600 (originally known as the Atari VCS) was Atari's first foray into the gaming market. The 2600 was one of the most popular game consoles in North America and marked a significant point in gaming history. This was many people's first time getting into video games, and the console received many home ports of popular arcade games. It was the console that marks Activision's big break in game development and emerging as one of the first third party game developers. It was extremely easy to develop games for at this time, which was both responsible for its rise and fall.
Due to this, however poor quality control was responsible for its downfall, between too many companies trying to cash in on the hype (with some food companies trying to make games, even!) and others rushing to get high-profile games out (notable examples include Pac-Man and E.T.: The Extra Terrestrial) this ultimately resulted in the North American video game market crashing for the first time in 1983. Atari actually buried several of these unsold game cartridges in a landfill in New Mexico shortly thereafter, leading many to visit the site and the creation of a documentary on the event.
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.