Magnavox Odyssey 100 and 200 (1975)
Most gamers remember Atari's Pong for getting the whole video game console party started back in 1975. Most do not know that Pong was stolen from an even earlier console, the Magnavox Odyssey (Pong was a ripoff of their Table Tennis game). Magnavox even sued over it, and reached an out-of-court settlement in their favor.
But nobody bought the Magnavox Odyssey, mostly because a primitive public that was frightened and confused by electronics thought that the Magnavox game console would only work on Magnavox televisions. So Atari utterly dominated the industry instead, delighting an extremely easily entertained nation.
Pong. Note TVs only had three channels back then.
A bitter Magnavox was looking to score some more of that Pong cash that everyone was rolling in. So in 1975 they cranked out two new versions of the Magnavox Odyssey: the 100 and 200.
"Now even more orange!"
Magnavox really wasn't thinking big, and figured that Pong would be the only video game ever. So they released consoles dedicated to very slight Pong variations, amusingly called things like TENNIS and HOCKEY (the two that were on the Odyssey 100--the 200 model had a third game).
Tennis, football, and hockey. Seriously.
Why you've never heard of it:
To give you an idea of what the technology was like at the time, the Odyssey 200 was not smart enough to keep track of your score. You had to do it yourself, with a manual slider thing (even Pong kept score for you, on-screen). Copyright laws were very loose in the gaming world at the time, and Pong rip-offs pretty much flooded the market. There was no reason to buy this stupid thing that made you keep your own score.
"Finally, something that combines the excitement of tennis with my passion for writing down numbers."
Despite dismal sales, Magnavox kept plugging away, later releasing even more consoles with even more variations of pong (the Odyssey 300 and 400, finally including the amazing innovation of on-screen scoring).
If you're one of those late adopters and would like to get in on the Odyssey 200 fun, you can usually find them on eBay for almost nothing (we found one at ten dollars with zero bids). Hook that shit up to your 72-inch HDTV and you've got yourself a party.
The Fairchild Channel F (1976)
This was released in August 1976 under the incredibly vague name "Video Entertainment System." Predictably, this name turned out to be too similar to another console, the Video Computer System released by Atari around the same time, so Fairchild was forced to change the name to the Channel F. Atari then changed the name of their system to the Atari 2600, but Fairchild didn't bother changing theirs back because, really, what would be the point.