Battletoads:
NES (1991 in North America & Japan, 1993 in Europe and South America, published by Tradewest in North America and Europe, published by NCS in Japan, and published by Playtronic in South America),
Genesis(1991 in North America, 1993 everywhere else, developed by Arc System Works, published by Tradewest in North America & Europe, published by Sega in Japan, Australia, and Asia, and published by TecToy in South America),
Game Boy[as Battletoads in Ragnarok World] (1993, published by Tradewest),
Amiga(1992, Europe only, published by Mindscape),
Amiga CD32(1994, Europe only, published by Mindscape), &
Game Gear(1993 in North America and Europe, 1994 in Japan, developed by Arc System Works, published by Tradewest in North America, and Sega in Europe & Japan).
(^NES, courtesy of The Gamers Dungeon)
Battletoads:
Game Boy(1991 in North America, 1993 in Europe, and 1994 in Japan. Published by Tradewest in North America & Europe, and NCS in Japan)
(^at least I hope that's not Ragnarok World, courtesy of Pinterest)
Battletoads in Battlemaniacs:
SNES(1993 in North America, Europe, and Australia, 1994 in Japan, Published by Tradewest in North America & Europe, published by Nintendo in Australia, & published by NCS in Japan), &
Game Gear[just "Battlemaniacs"](1993, South America only, published by TecToy)
(^SNES, courtesy of Pinterest)
BattleToads:
Arcade (1994, published by Electronic Arts)
Battletoads/Double Dragon:
NES(1993, published by Tradewest),
Genesis(1993, published by Tradewest in North America, and TecToy in South America),
SNES(1993, published by Tradewest) &
Game Boy(1993, published by Tradewest in North America and Sony Imagesoft in Europe)
(^Genesis, with some sort of HD filter through an emulator, courtesy of gamefabrique)
1-2 players(handheld versions 1 player only)
They all pretty much control the same, one button attacks/picks up weapons, the other jumps, combine the 2 for a jumping punch/slash(the latter being much more effective). How much of it remains a beat 'em up depends on the game, but realistically speaking, the arcade game and the Double Dragon crossover are the 2 major reasons for this thread. Most of these games veer off into other directions with vehicle/racing portions, rappelling sections, obstacle courses, shooting, even flat out platforming. In all, it's mostly a very challenging, general action series of games.