For games that involve zombies -
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by Osanagocoronokimini (they have a bunch more zombie related games but thats the only one on this site)
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by Seacoxx (it has a sequel too)
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by Siren's Domain (RPGM game still in development but is pretty alright)
As for games that involve ghosts? I can't think of many of the top of my head. There's a couple of yuri ghostly VNs on the site, but I cant remember their names unfortunately