So this isn't a "unique" console but I didn't put it in the Other Clones category because it was made by Sega themselves. It's a very rare Megadrive (Genesis) variant, in the Compact style similar to the SMS Girl or Sega Nomad without a screen. Has to be hooked up to a TV (thereby not making it a real "portable") and outputs to standard AV, which means it should work in most televisions.
Very few of these were sold outside of Japan (I don't think it was ever officially released anywhere else.) A lot of these ended up being sold to different airlines for passengers to use. Has the 1st player controller built in and a hook-up for a 2nd player on the side. Don't know if it works with the Sega CD, 32X, or all the other baloney. Rare but not impossible to find, expect to pay about $80 -$150 depending on box and condition.