NEC's PC-88 and PC-98 series of home computers were very popular in Japan in the 1980's and 1990's. There is very little information about the first versions of the game in English, but as far as I can figure out, the original Popful Mail was created by Falcom for PC-88 in 1991, and updated for the PC-98 in 1992. Both computers' technical capabilities were naturally much inferior to the Sega CD or Super Famicom. This is most obvious with the graphics, which now look rather dated. The character's are very small, and animation is far from smooth. Even so, the intro and cut-scenes look surprisingly good (at least on the PC-98). Music works reasonably well too, even though sound quality is much inferior to later systems. The tunes are pretty much the same as in the Sega version.
Stage design and structure is pretty much the same as in the Sega version, with some small differences. The story's the same as well, although it's all in Japanese, so I can't say much for sure. The names of some of the characters are different in the Japanese versions. Muttonhead, for example, is Material.
What most separates this game from the Sega version is the combat system. You don't slash or shoot at opponents with an attack button. Instead, you simply run or jump into them. This takes a little getting used to... Other than that, and the much inferior graphics, the game is actually quite similar, down to menus and everything. Still, to fans of the Sega version this is mostly just a curiosity. Recommended for true retro fans.
(More screenshots here.)
The PC-Engine, also by NEC, was a popular video game console in the late 80's and early 90's. In the West it was known as the TurboGrafx-16, but it never became as popular as in Japan. The console was also the first to have an optional CD drive, allowing for much greater storage capacity. The PC-Engine version of Popful Mail is basically an updated version of the PC-98 game, with better graphics and sound. The CD format also made it possible to add voice acting and anime cut-scenes.
In 1994 Sega ported the game to its Mega CD console. This version featured graphics much superiour to both NEC versions, as well as lengthy anime sequences and voice acting. In addition, the gameplay was changed. Instead of the running into enemies type of combat in the original version, this game had a more traditional way of attacking by hitting the attack button. Other than that, the basic level design, overall structure and story were pretty much the same.
Working Designs brought this game to America, where it was released in early 1995. The game was translated into English relatively freely, making it even funnier than it was. Working Desings took a lot of effort to make the voice acting as good as possible, and the total of two and a half hours of voice acting, together with a whole twenty minutes of anime sequences, remains one of the best parts of the game. Working Designs also made many little technical changes to improve the game. Among other things they added some voice-acted events that were previously only text. They also made it more challenging (though some could argue that some spots are a touch too challenging). This is the only version that was translated into English. Lucky for us, it's also the best.
(For more screenshots see the gallery section.)
Super Famicom is of course the Japanese name of the famed Super Nintendo Entertainment System. The game was ported to this system by Falcom in 1994. This version, even more than the Sega version, is like a whole new game. The gameplay was, as in the Sega version, more on the lines of traditional platforming. There are a couple of differences from the Sega version, such as the ability to crawl. The graphics were redone as well, and are reasonably high quality for the SNES (although I would argue that the Sega version looks better). The music, although the SNES sound chip was more advanced than Sega's, doesn't seem quite as good on the whole. Due to the much more limited size of the cartridge, this game naturally lacks the voice acting and anime scenes of the CD versions.
While the overall story and structure remains the same, the levels have been entirely redesigned. A lot of detail in plot development has been changed as well. Gameplay doesn't seem as smooth as in the Sega version, and the game is also quite hard. It's difficult to avoid being hit. I admit I haven't tried this game much, but I couldn't really get into it the same way I got into the Sega version. Even the PC-98 version seemed more fun...
(More screenshots here.)