The Speak and Spell, which was first shown at CES in 1978 and sold in 1979, was one of the first gadgets with a visual display to use interchangeable game cartridges, and it taught a whole generation how to spell.
Basically, you could get word packs to pop in the back, bringing new games and new vocab to your kid so they wouldn't hassle you to teach them words when you're just trying to watch Monday Night Football. It used a speech synthesizer to say the words out loud so the kids knew the correct, if a bit robotic, pronunciation.
Here's an ad, from the early 80s:
And of course you can't forget the ridiculous circuit bending that hackers have done with these things in the years since, making them way more fun and entertaining. Just check this shit out:
Gizmodo '79 is a week-long celebration of gadgets and geekdom 30 years ago, as the analog age gave way to the digital, and most of our favorite toys were just being born.