Mattel, as you all no doubt know, wasn't much involved with computers or electronics - their main sellers of the 1970s were of course Barbie Dolls and Hot Wheels cars. I know this because my sister had loads of Barbies (and Pippas and Sindys for that matter :) while I was into the Hot Wheels stuff with its bendy orange track and the capability of the cars to go though plate glass windows after a track run down the stairs :oD

However, they saw what Magnavox and Atari were doing and wanted a bit of that for themselves. Originally the plan was to make cartridges for these systems, but nobody was interested so Mattel went ahead and came up with the Intellivision. Released in 1979 it was a good machine for its day with lots of colours on-screen and an attractive case. It sold really well because most of the games were Sporting simulations rather than ack-ack-ack or pong types, and it was really the only system to target (sorry :) such an audience. It was let down slightly by the difficult-to-use disk-type controllers, but that was a minor aside. Additions such as the Voice Synthesizer (a really good one according to people who have compatible games) added to the fun.

However, things started to go askew. The success of the Intellivision prompted Mattel to look for a home computer design to build under their own name, and they selected Hong Kong's Radofin as a partner. Radofin were already well known for their pong consoles that were rebadged or rebuilt by the likes of Prinztronic, Grandstand, Acetronic, Videomaster and Interton. However, the computer design that came from them left a lot to be desired.

The Aquarius (for that was its name) was grim to say the least - 4K of RAM with less than 2K left for the user, a BASIC without such niceties as the FOR-NEXT loop (initially), awful chiclet keyboard that was worse than the Spectrum's 'dead flesh' job and only 4 colours on screen at once. It was also too expensive at $200. The machine was so poor it was only sold for 3 or 4 months before Mattel pulled the plug and basically paid Radofin to let them out of the contract. At roughly the same time Mattel also gave up on the Keyboard addon they'd produced for the Intellivision. Again it was too expensive at $700 and unreliable.

Mattel jumped ship from Electronics and probably because of that are still around today in one form or another. The Intellivision engineers left and formed a company called INTV that produced what would've been the Intellivision II as the INTV II and Radofin developed a followup to the Aquarius which didn't improve much on things - 20K of RAM, slightly improved BASIC and a real keyboard but it was too little too late and not very many were produced.

Aquarius
Aquarius 4K expansion, boxed NOS (new old stock), ie unopened
Aquarius 16K expansion, boxed NOS
Mini-Expander for Aquarius with Intellivision-style controller
Intellivision - boxed in excellent condition with power cord, aerial lead and user guide.
Intellivision on its own but in better condition.
Intellivoice voice expander module, boxed mint.
Intellivision Computer Adapter with PSU
Intellivision Music Keyboard, boxed in excellent condition
20 boxed games with manuals and overlays

Skiing
Basketball
Major League Baseball
SNAFU
Soccer
NHL Hockey
Tennis
Armor Battle
Frog Bog
Lock'n'Chase
Super Cobra
TRON Deadly Discs
NFL Football
Nightstalker
PBA Bowling
Astrosmash
Sharp Shot
Golf
Space Battle
Las Vegas Roulette
Utopia
Reversi
Buzz Bombers
Shark! Shark!
Advanced Dungeons & Dragons
Horse Racing
Las Vegas Poker & Blackjack
Royal Dealer
Star Strike (u/b)
Dragonfire (u/b)

Intellivision Lives! - the official Intellivision website