As one of the Xonox "Double Ender" cartridges, this features Robin Hood and Sir Lancelot. Each of the two games was released separately, though it's generally more common to find them in this form. This particular double-ender is the most common to feature either of these games.
The Double-Ender is two games in one - each end of the cartridge has a different game. These cartridges are about 2.5 inches longer than a standard cartridge, and the case is wider in the middle. There is one long label that is typically blue, with game art for both sides split diagonally down the middle. Titles are printed in red text against a yellow banner. All the titles found on the Double-Enders can also be found in standard single-ended cases.
Xonox, based in Minnesota, started developing Atari cartridges during the height of the 2600's popularity. They contributed many high quality games available for the early platforms. Xonox capitalized on the novelty and perceived value of "double-ender" cartridges. These could be inserted into the console on one of the two ends, each end offering a different game. Different double-ender configurations could package the same game with different counterparts. Xonox was not the first company to try this; Playaround did it earlier with their adult-themed titles. Xonox eventually abandoned this idea and began releasing single versions of some of the titles previously offered as double-enders as well as a few new titles.
Xonox was one of many small video game companies to fold during the Video Game Crash of 1983.