The method of expanding a video system via game cartridges—still employed by today's handhelds Nintendo DS and Leapster—was first introduced in an obscure home system called the Fairchild Channel F. Released in the nebulous period after the glut of home pong copies, but before the Atari VCS, The Fairchild boasted some significant firsts for the home market. In addition to being the first system to utilize game cartridges, it was also the first home system that allowed 1-player gameplay against the computer; all previous home systems required 2 players.
Dial F... ...for forgettable
The Fairchild Channel F eventually released 26 cartridges. Despite being the first of its type to market, it made only a blip (perhaps also a bloop) on the radar of videogame history. Having only half the RAM of 1977's Atari VCS (64 bytes) and games that were widely-regarded as "not much fun," the system died with little notice; few attended the funeral. In this video, The Irate Gamer, takes a humorous look at the Fairchild's dreary entertainment offerings.
Bonus points. If you enjoyed that video, be sure to check out Episode 3 of the Irate Gamer's History of Videogames, which uncovers the mid-70's coin-op hits you've never heard of, including Combat for Atari - a coin-op port of Tank.