The first Raiden (or as it was somtimes known; "Raiden Trad") was relased in 1990 by Seibu Kaihatsu*, a Korean based company with three different localizations. It was later ported to the Turbo Duo, SNES, & Gensis.

Raiden II was relased 3 years later in 1993, with much of the same impact, but many people complained that the improvements were lacking ("I waited three years and all I got was a purple trace lazer?!"). The game was later ported (2 years late mind you) onto the windows platform.

Raiden DX, relased one year later in 1994 added vast improvements (as compared to Raiden II). The game utilized three buttons (fire, bomb, & rapid fire) as compared to the defacto standard two buttons Raiden and Raiden II utilized. The graphics were also on par with other games of the same genre (shooters). Raiden DX was later ported for the Playstation.

Raiden Fighters was relased 2 years after Raiden DX in 1996, and to fans was considered '...a step back and forward'. While new features were added (like mutiple ships and much more stunning graphics), features like rapid fire were removed. To my knowledge, Raiden Fighters was not ported to any console or computer system.

Raiden Fighters 2: Operation Hell Dive, relased in 1997 is, for lack of better words - amazing. The technical detail added is above par, however - I'm only aware of this being avable in some arcades.

The final** game in the Raiden series is Raiden Fighters Jet (Taking a page from the World Heros series trick book it would seem). Raiden Fighters Jet, relased in 1998 was much of the same, pretty explosions, pretty ships - prettyness all around. To my knowledge, this has also not been ported.

The Raiden games have much been a bane of the emulation community, for after the first game massive encryption techniques were implemented - which is a shame really, as some of the games are beging to disapear. If you find a PCB on ebay for any of the games, I'd recomend it, there all excellent (nit-picking aside).

* = Seibu Kaihatsu made all the games, however different companys published or ported the games (/msg me if you know them).
** = 'Final' is a risky word, chances are they'll be more.