Open Library
Horror
Fear is the oldest story.

Recess is a jungle!
Jack Chabert

Stories New and Old
Hamilton Wright Mabie

The gold bug, The purloined letter, and other tales (Eleonora / Gold-Bug / Purloined Letter / Tell-Tale Heart)
Edgar Allan Poe

Slaughter in Barnaby Close
Michael Cargill

Temperature
Adam Santo

The Best Crime Stories Ever Told
Dorothy L. Sayers

Her Soul for Revenge
Harley Laroux

Intercepts
T.J. Payne

Mapping the Interior
Stephen Graham Jones

Classic Short Stories
Alphonse Daudet

The Woods All Black
Lee Mandelo

My Darling Dreadful Thing
Johanna van Veen

Straight
Chuck Tingle

Monstrilio
Gerardo Sámano Córdova

The Vampire King
Michael A. Martin

Thaw
Bryan Dunn

Clive Barker's A-Z of horror
Clive Barker

Moon of the Crusted Snow
Waubgeshig Rice
Tales (Cask of Amontillado / Descent Into the Maelstrom / Fall of the House of Usher / Gold Bug / Ligeia / Masque of the Red Death / Murders in the Rue Morgue / Pit and the Pendulum / Purloined Letter / William Wilson)
Edgar Allan Poe

Stay Out of the Shower
William Schoell