Micronauts are the US/UK version of the Japanese Microman figures and Palisades is reissuing them and updating him. In Japan Microman begat Microchange. And from Microchange there came a number of transforming toys who along with some similar toys from Diaclone created Transformers. Micronauts were originally available in the 70s, and were out slightly prior to and contemporary with the earliest SW toys. IIRC they were released over here by Airfix ?
The reissue figures - like some of the originals - are available in several colours: Using http://www.bigbadtoystore.com/images/pl010big.jpg we'll work down from the top. All the figures come with stands.
Time Traveller (top row): Mine's clear with gold chrome. A humanoid figure with some chest armour. 2 joints at the shoulder (both fwd & back and side to side, elbow, wrist, hip, knee and ankle on each side, plus a waist and a ball jointed head. If you've got a GI Joe or Action Force figure this will be familiar to you even down to the O ring elastic band I can see inside. Unfortunately there's a design ooops on this one in that the elastic band inside ends up twisted and so he tends to one side. The accessories here are 5 interchangeable chest panels and an L shaped piece of plastic that fits into a hole in his back, which is slightly large than that on the aforementioned GI Joe figure. Not a lot to write home about but this was where they started...
Membros: This is a much later figure from the original line, one of an alien subline. Same articulation, same back panel hole. He's got a backpack, with a cable, which can be connected to one of 2 weapons. The different coloured brain piece can be removed (and swapped between Membros) and the weapons can be substituted for his hands. The build quality on mine isn't great - legs have a visible seam down the middle, the back pack doesn't fit snugly - it does on other figures so I can only conclude that the hole in his back is too big ! - and there's some quite visible marks where the figure has been detached from the tree....
Space Glider: A similar looking figure to the Time Traveller - mine's in blue and black - but with a clearish smoked grey helmet, a gun and rocket pack with wings that pop up at the touch of a button. Same articulation, same back panel hole that the glide pack plugs into. The shock came when I picked this up - it was cold and heavy ! That's right, die cast metal right the way through baring the head and hands. I'm impressed,
Acroyears: Red, Black and clear plastic. I'll get the moan out the way first - there some more bad tree separations here, and a very bad paint scratch on the chest. Moan done. I love this figure ! More metal in the chest, a removable head - I recall this from the Giant Acroyear I had as a kid, oooh the arms and feet come off too. A fantastic back pack and a big sword :-) For some reason there's also a bird thing.....And the huge boots conceal wheels so you can roll him along hehehe. Ah ! Now I recall what the bird is for ! He's a transformer ! Plug the wheeled feet into the tips of the wings underneath and mount the bird thing on the ankles to form something not unlike RID Obsidian. Have a look at http://www.innerspaceonline.com/acro.htm
So..... why is Megatron here ? Well as I said Micronauts was the English form of Microman which begat Microchange. Microchange had a number of household objects that turned into robots - including 2 different tape players, a number of tapes, a microscope, a camera and a gun ! (and a number of small cars) The gun went on to be Megatron. ( see http://www.microforever.com/1981_the_big_reset.htm ) His accessories as we all know form a cannon for him to use. If you look on the stand on the cannon (formed from the arm rest) it's made of 2 pieces. Remove the top piece and slot the gun back into the bottom bit. The loose bit of stand slides into the back of the cannon forming a chair for your Microchange figure to go it...... or Microman..... or Micronaut ! There's a protruding post which fits the hole in the Micronaut's back. Now effectively Acroyear's boots get in the way, Membros' post hole is too big and Space Glider is a bit heavy with all the metal so if you want to try this get a Time Traveller.
Else go for Acroyear or Spaceglider, they're cool !