dagger
Adventurer
Just go to the official fan sight and get the in progress Dark Sun conversion:
http://www.athas.org/
http://www.athas.org/
I'm not sure you have to go that far. In fact, I think you later get at all you really have to do:Take a regular world (FR is especially good for this). And then change it a little bit:
The city of shade appeared above Waterdeep, conquored and enslaved it. Baldur's gate's merchant lords have subverted the rest of the area. Efreet have returned to Calmishan. The red wizard's trading enclaves have enabled them to take over many smaller regions where they rule discreetly as puppet masters. Etc.
The idea of Szass Tam using Elminster:s heart as a ritual focus is probably almost as creepy as putting people into a real ravenloft game.
I don't think there's any need to rewrite the setting. Just reduce how much magic gets tossed around, and give most magic items a dark side.In general less divine magic (cures, etc) and more monsters the PCs can't hurt the more grim it gets. (Monsters that can only be hurt by the weird black magical dagger that slowly turns the PCs flesh blue, eyes yellow and gives her an uncontroable craving for brains is also good).