Howard Philips Lovecraft is largely known for authoring such classic works as The Shadow Out of Time.  He is less known for horror stories he had a hand in, through his revisions and collaborations with other authors. 

In many cases, the product of Lovecraft's ghostwriting achieved little success.  

However, some of his collaborations merit our attention.  That part of Lovecraft's work falls under one of two headings.  I'm borrowing primarily from The Horror in the Museum, 2007.  In one case, Lovecraft re-wrote so much of the story, that aside from the original author's name, it was a HPL work.  In the second set of stories, Lovecraft acted more as a regular editor: he corrected language, syntax, and punctuation.  What I want to do is to provide two lists from the aforementioned reference.

Primary Revisions -  Major HPL Rewrites:

  1. The Green Meadow (Elizabeth Neville Berkeley and Lewis Theobald, Jun.,  1918/19)
  2. The Crawling Chaos (Elizabeth Neville Berkeley and Lewis Theobald, Jun., 1920/21)
  3. The Last Test (Adolphe de Castro, 1927)
  4. The Electric Executioner (Adolphe de Castro, 1929)
  5. The Curse of Yig (Zealia Bishop, 1928)
  6. The Mound (Zealia Bishop, 1929-30)
  7. Medusa's Coil (Zealia Bishop, 1930)
  8. The Man of Stone (Hazel Heald, 1932)
  9. The Horror in the Museum (Hazel Heald, 1932)
  10. Winged Death (Hazel Heald, 1932)
  11. Out of the Aeons (Hazel Heald, 1933)
  12. The Horror in the Burying-Grounds (Hazel Heald, 1933/35)
  13. The Diary of Alonzo Typer (William Lumley, 1935)

Secondary Revisions - HPL acts as an editor:

  1. The Horror at Martin's Beach (Sonia H. Greene, 1922)
  2. Ashes (C.M. Eddy Jr., 1923)
  3. The Ghost-Eater (C.M. Eddy Jr., 1923)
  4. The Loved Dead (C.M. Eddy, Jr., 1923)
  5. Deaf, Dumb, and Blind (C.M. Eddy, Jr., 1924)
  6. Two Black Bottles (Wilfred Blanch Talman, 1926)
  7. The Trap (Henry S. Whitehead, 1931)
  8. The Tree on the Hill (Duane W. Rimel, 1934)
  9. The Disinterment (Duane W. Rimel, 1935)
  10. "Till A' the Seas" (R.H. Barlow, 1935)
  11. The Night Ocean (R.H. Barlow, 1936)