Dungeon Explorer
Probably the least forgotten about game of the bunch, Dungeon Explorer was developed by Atlus and released in 1989 for the TurboGrafx-16. It combined Gauntlet-like gameplay with action RPG elements akin to Secret of Mana, allowing as many as five people to join forces as they search for the missing Ora Stone. Of course, in order to play with the full roster of five characters, you had to have the sold-separately Multi-tap accessory. Odds were if you had a TurboGrafx-16 you didn't have that many friends in the first place. (Does that count as a retro burn?)
Ancient console wars aside, Dungeon Explorer got a new lease on life when it was released on the Wii Virtual Console back in 2006/2007. Two related games were pushed out in Japan around this time. They were later localized and released for PSP and DS in North America as Dungeon Explorer: Warriors of Ancient arts and Dungeon Explorer in Europe. Two player co-op was possible via wireless play, but because the game didn't get a very warm reception, nobody was around to play with you. TG-16 all over again.