The handheld version of Zaxxon is a portable LCD game manufactured by Bandai with a license from Sega. It was released in 1982, and is based on the arcade game, Zaxxon.
This system uses a "double panel" LCD screen, one to simulate the first section of the game (set in space) and another for one of the space stations. Aside from a similar perspective, handheld Zaxxon is very little like the arcade game - the player cannot move upwards or downwards, and many of the memorable scenery in the game (such as the brick walls and turrets) were omitted due to hardware restraints. In essance this turns Zaxxon into a fairly standard LCD shoot-'em-up game, where players move left and right shooting foes before being hit.
The handheld version of Pengo is a portable LCD game manufactured by Bandai with a license from Sega. It was released in 1982, and is based on the arcade game, Pengo.
Very little is known about the LCD version of Pengo, though it is possible that it was not released outside of Japan. It can be assumed it bears some relationship with the arcade game, but as the system is quite rare, nothing has yet been documented.