The Microvision was the very first handheld game console that used interchangeable cartridges. It was designed by Jay Smith, the engineer who would later design the Vectrex gaming console. The Microvision's combination of portability and a cartridge-based system led to moderate success. It was released on October 1st 1979 for $49.99, which would equate to $166.55 today.
An exact day for the Microvision release could not be found, but sources point to November of 1979.
October 1st, 1979 Source: psp.about.com
Came with the Block Buster game.