Mattel's first, but oddly enough not their last console. Releasing sometime in 1979 for the US, the Intellivision was the firm “2nd place” behind the Atari 2600, but was unable to challenge the 2600's position in sales. Specifications-wise, however, the Intellivision is reasonably capable, featuring a GI CP1610 CPU, 1 KB of RAM, and a resolution of 156×96 + 16 colors.

https://en.wikipedia.org/wiki/Intellivision

ECS EXEC/BASIC ROM (system BIOS and built-in BASIC programming)

Yet another BASIC cartridge available for an early game console, plus the keyboard's BASIC which apparently needed to be separate.

Not much to say about this (it's a very primitive “DOOM”), but it is technically impressive for this console.

http://spatula-city.org/~im14u2c/intv/doom/

This is a simple Breakout clone that compiles Java .class files with Java Grinder and assembles with naken_asm

Through the power of the JIT compiler esque Java Grinder by Mike Kohn, it is now possible to run Java programs on the Intellivision. Amazing! Of course, these programs need to be specifically written for the Intellivision.

https://www.mikekohn.net/micro/intellivision_java.php

For general information, see the Game Console Revisions Overview.

There are three versions of this console, arranged chronologically.

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Being the first revision, this revision is also the largest in footprint. The controllers are hardwired with short and coiled “landline” style cords, and they are not very easily removed. Controller number pad buttons are physically indented. There’s wood grain on the front.

The entire console is now colored in white within a much smaller footprint, with controllers that are now detachable with longer cords. However, the controller number pad buttons are now a flat surface, making blind usage less convenient. Within the cartridge slot, a video input is now accepted, enabling the usage of various addons such as the System Changer (Atari 2600 compatibility). Lastly, internal technical changes with the sound chip and ROM resulted in a few games not working on the II, and a few games having minor graphical or sound glitches.

Here, console sizing has returned to the original design, while also bringing back the hardwired controllers, despite the fact that the controller design is still of the II’s. The color scheme has been changed to all black and silver.

There are no revisions within any version. BEST RELIABILITY and RECOMMENDED OVERALL couldn’t be assigned.

https://en.wikipedia.org/wiki/Intellivision#Intellivision_II

https://gametrog.com/intellivision-1-2-3-information-specs/