UNNATURAL SELECTION / Maxis / PC
Maxis snuck this game out in the heyday of the various "Sim" games. It was pretty obscure even then, but has now virtually disappeared from existence, save being hosted on a couple of abandonware sites. Sans manual, and no one ever seemed to make a walkthrough for it that I can find, meaning you're stuck figuring out how to play it on your own.
Which is nearly mission impossible, because the game is pretty dense, the interface is not self-explanatory at all, and there's no in-game help or instructions of any sort. The basic idea of the game is to breed monsters, using three basic "stock" types who each have a particular characteristic - strength, speed or vision. By using radiation to mutate their genes, breeding them together, using food and walls to control and separate them, you aim to create offspring that are better fighters than their parents.
There's a "story mode" of sorts that establishes you are a geneticist grabbed up by the military to create these creatures to fight against another rogue geneticist who appears to have taken control of a series of small islands using her own army of monsters. Apparently you hop from island to island battling her monsters by creating your own mutated freaks. I say "apparently" because the game is so obtuse I really couldn't figure out how to do anything with it. It's not even clear how the monsters are arranged, or how to induce them to mate or whatever, or if any of your radiation baths are having any kind of an effect at all. There's a game clock that passes in semi-real-time, and every now and then your research assistant pops up in a cut-scene to inform you of some new development or another, so I assume if you sit around long enough the evil bitch attacks and overruns your lab with her hideous army or something. I dunno, I couldn't be stuffed to sit around that long. There's an "independent mode" to just play around in without the story mode pressure, but I didn't find it any more helpful at all in understanding what the hell I was supposed to be doing.
The game's presentation is pretty spartan, and it looks like it was on a thin budget, but I did appreciate how they captured the spirit of corny 1950s monster/disaster movies with digitized pictures and appropriate voice acting in the cutscenes. Your research assistant sounds notably like Otacon. I wish I could find credits to see if it's the same guy (it's not on his imdb page, but it could have been too minor or obscure to be included, or he may have been using a pseudonym for actor's guild rules or whatever.)
I chose not to rate this one given that the game did intend for you to have a manual, which presumably would have shed at least some light on how to play the damn thing. As it is right now, however, with no official re-release, no manual or walkthrough that I could find anywhere, and an extreme scarcity of even the most basic information about it on the web, it's virtually unplayable.
* Here's where I found it
* About all the more information there is anymore
* Gameplay Video