The Atari Flashback 2 and 2+ are literally shrunk down Atari 2600s with 40-something built in games, including homebrews, Activision games, Atari classics, and brand new original games. They even have instructions silk-screened onto their PCBs for the user to add a real 2600 cartridge port. They are compatible with original controllers and accessories and they even have composite video output, much better than the stock RF out on those old systems. And of course, the new controllers that came with the Flashback systems work with original systems.
But only the 2 and the 2+ are real hardware. Any and all other Atari Flashback units are emulation based, with the first being the worst by far.