Masque of the Red Death
A spin-off to Ravenloft, Masque of the Red Death (named after Edgar Allan Poe's short story of the same name) basically is what you get if somebody at TSR goes "Okay, Ravenloft is pretty Gothic Horror, but how can we turn it up to eleven? I know, let's put the PCs in a world that's our own Earth in the 1890s, but monsters and evil magic are real!"
The basic story is that, on "Gothic Earth", a malevolent and corrupting entity called the Red Death, hinted to be akin to the Dark Powers of Ravenloft (and confirmed by the creator and an early preview to be one exiled for breaking some rule the rest had), has been messing around and fouling up the world for centuries, trying to plunge it into eternal (spiritual) darkness. Your players are brave, bold Victorian souls who dare to seek out that which is going "bump" in the night.
Masque of the Red Death uses proprietary classes. These classes are generally of lower power than the normal classes. Casting is also massively nerfed by making all spells past first level take another round to complete and making them all risk corruption. Both 3rd edition based variants also gave these classes the problem of not being full classes, with the vast majority not gaining class features past a certain level.
Unfortunately, the setting was released before it became trivial to research the 1890s online and was never very popular. Despite this, it did get both three adventures in Dungeon Magazine, a few Dragon Magazine expansion articles, an RPGA Campaign (which, notably, has an actual conclusion to the setting), and two official Dungeons & Dragons 3rd Edition updates (the first from that RPGA campaign, and the second from White Wolf when they had the Ravenloft license). There's also a DM's Guild product updating the game to 5E, cleverly exploiting the fact it's officially part of Ravenloft instead of its own setting to bypass the setting restrictions on content for that scheme. Time will tell if it does any better in an era where primary sources are trivial to obtain as public domain e-books.
- Dragon #215 - Donning a New Masque - new kits
- Dragon #236 - Mystics, Miracles and Meditations - new kits
- Dragon #240 - Mysterious Cities - brief blurbs about eleven cities, with both mundane and mystical goings-on
- Dragon #245 - Seeds of Evil - more history about Gothic Earth and a new monster
- Dragon Annual #2 - Villains of Gothic Earth - eight unique villains, each based off a monster
- Dungeon #61 - Jigsaw - a flesh golem runs amok in Switzerland
- Dungeon #67 - Fall's Run - the players encounter the occult when their train is forced to stop for the night in Fall's Run
- Dungeon #71 - Dark Magic in New Orleans - a murder mystery with Marie Laveau