Back in the early/mid 20th century, pulp authors didn’t conform to genre norms like they do today. The rarely-reprinted tales in these collections (by masters like Poul Anderson and Edmond Hamilton) imaginatively mix fantasy and sci-fi elements. The five books included in this bundle:

Swordsmen from the Stars by Poul Anderson (three novellas from Planet Stories)
Twilight of the Gods by Edmond Hamilton (eight stories, mostly from Weird Tales)
The Avenger from Atlantis by Edmond Hamilton (eight stories from Weird Tales)
Planetary Adventures edited by D.M. Ritzlin (five stories by Anderson, Hamilton, Henry Kuttner, Ross Rocklynne, and Bryce Walton from various pulps)
Lands of the Earthquake by Henry Kuttner/Under a Dim Blue Sun by Howie K. Bentley (in the style of the old Ace Doubles)