ToME WikiNerdanelVampire: This is an original module idea in the sense that it isn't based on anything specific.
Background
The forces of darkness have won. You were among those few that still resisted their new masters. Now you are dead, and the Dark Lord has cursed you to a horrid unlife as an example to the others. You are expected to eaten by scavengers in a short order or watch as you slowly and hideously rot away, but you are determined find a better way.
You start in the graveyard, accompanied only by your meager burial gifts. You will need to fight things like hungry rats, graveworms, and even graverobbers before you get into the town and can go shopping. Then you can go to level up in the vast graveyard and eventually seek new dungeons until you are powerful enough to challenge the great evil of your world.
Races
Corpse is the starting race. Its greatest weakness is that it will rot. This means that at intervals you will lose a point from a random stat unless that stat is sustained.
Luckily for you, it is possible for undeads to become more than walking corpses. Certain ancient tablets describe the secret rituals undeads can use to gain a greater form than before. These tablets have been lost and you need to find the one you want in the dungeon before you can use it.
You can transform yourself into a Zombie, a Ghost, or a Vampire, depending on whether you value our body or mind or try to keep them both. Later you can transform into an even better form, but your initial choice constrains you, as well as your sense of morality, for some of the rituals you need to do to become more powerful are things of purest evil and can warp your mind if you attempt them.
Zombie
Zombies are strong and dumb. They still rot, albeit at a reduced speed from a Corpse. None of the forms derived from Zombie rot at all.
Skeleton (good) is fast and dextrous.
Sludge (neutral) has many hitpoints and two (three?) weapon slots. As it is formed from your liquedified flesh, it cannot wear most armor.
Deathknight (evil) is a powerful, mummified warrior that also has some intelligence.
Ghost
Ghosts are smart and weak.
Spectre (good) can walk through walls at the cost of hp and has a full ESP but is physically extremely weak.
<Elemental> Spirit (neutral)
Shadow (evil) is a powerful and terrifying creature of darkness.
Vampire
Vampires are both strong and smart, but they are vulnerable to daylight and need the blood of the living to sustain themselves.
Daywalker (good) has no problems with the daylight.
Shapeshifter (neutral) can transform temporarily into various useful shapes.
Nosferatu (evil) is like a normal vampire but more powerful.
Monsters
There are lots of different monsters, including numerous undeads. The good/evil/neutral designations above do not necessarily apply to the monsters since they could have been evil to start with.
Winning the Game
You get a different ending according to whether your form is good, evil, or neutral.
Good: You have destroyed the Dark Lord forever. The world is free. You can now use your powers and reputation to heal the wounds of the war and to bridge the gap between the living and the undead.
Evil: You have vanquished your greatest rival. You exalt as your new dark minions look at you in shock and terror. You will be obeyed forever.
Neutral: The Dark Lord is destroyed and his minions will now turn to fight themselves. You suppose [<the highest-level surviving unique>|the forces of good] will probably win, but you never know... You smile as your vengeance is finally achieved.
Chatter
DarkGod: Hey I like the idea of your corpse as a "stat" that can evolve. Interresting idea!
KhymChanur: Interesting. Does being good/neutral/evil have any effect on gameplay in and of itself, or is just that the different forms have different strengths and weaknesses?
NerdanelVampire: I meant the different forms to be something like the One Ring and its temptation. Real gameplay effects are not necessarily required, but could be nice. I think ideas like having most living monsters be coaligned to good forms and neutral to neutral forms could work.
Zonk: It's a very cool and refreshing idea, particularly the things about 'evolving'as DG said before me.
KhymChanur: An idea for a fourth branch of evolution: ghouls. Like vampires, they need sustanence to stay "alive", in the form of flesh. However, unlike vampires, ghouls are carrion eaters, so they can eat the flesh of long dead corpses and other undead, giving them a more plentiful suply of food. Ghouls are somewhere between zombies and ghosts, being moderatly strong and moderatly smart. To make up for not being great at any one stat, ghouls get extra benifits from eating corpses: temporary stat boosts and other temporary effects, gaining skills and abilities, healing damage, and so forth (what exactly is gotten from eating corpses would vary depending on the final good/neutral/evil evolved form).
Additionally, the evil form of the ghoul could have a "grave robbing" ability: walking secert, mystical paths which only ghouls can find, they can slip into and out of locked crypts and burried coffins. This gives them easy access to food, a place to hide (except from other ghouls), and they will also sometimes find valuables burried with the dearly departed.
Adam: I guess this could work, but if you want to base the whole thing on this evolving state of undeath thing, then you will probably need a whole lot more different forms, as well as a very large differences between the forms. I don't mean just stat and hitpoint differences, but something that really changes the flow of the game.
That sludge evolution, for example. It's liquefied flesh, but what does that mean in gameplay terms, except that it can't wear any armor? Does it get resistance to piercing weapons, because it's just a chunk of slime after all? Can you ooze under doors, through the cracks in thin (one-tile) walls, maybe flow around adversaries and switch places with them? Morph parts of your body into weapons, or drop fragments that then proceed to overgrow the current dungeon level like some Lovecraftian horror gone real? Also the other features of undeath. Will there be dungeons filled with poisonous gas that can't kill you because of your lack of metabolism? Will you be able to enter water, since you don't need to breathe? Should there be damage types that you are summarily immune to, or that affect you in a different way from living creatures, like Cold freezing you for a few turns, but not doing damage?
Personally, I think this might work great as a setting for a tabletop RPG. Unless you take stuff like that into consideration, though, you really won't get much more than ToME with undead-flavoured prestige classes. Try and make this a good one, because it really could be.
Sirrocco: Check out the SoUL page for a somewhat different take (inspired by this module, though I didn't remember at the time). Of course, ideas are *cheap*. The actual process of programming is the bit that takes the serious time and energy.