If you are specifically looking for free science fiction with biological themes – cloning, longevity treatments, unusual forms of reproduction, or featuring cats or squids – your first stop should be right here at the free science fiction with biology directory.
But if you are looking for a wider variety of science fiction stories, then I’d recommend you check out the following sites:
Amazon.com Bestsellers: Science Fiction for the Kindle :
Amazon.com has two science fiction best-seller lists for the Kindle: paid and free. The free science fiction offerings range in quality from not-that-great self-published novels to old classics to new offerings from major publishers. Many are available for free for only a limited time, so it’s worth checking the list every so often. Download of Kindle books requires an Amazon.com account and either a Kindle reader or installation of the free Kindle app on your Mac, PC, iPod, iPad, Android or other device.
And if the Kindle isn’t your thing, then there are a wide variety of podcasts and online magazines that regularly offer excellent science fiction stories to read or listen to. My favorite sources:
Escape Pod: science fiction podcast that includes fiction. Stories are often reprinted on the site itself.
StarShipSofa: science fiction podcast that includes fiction
Clarkesworld Magazine: magazine with original stories
Lightspeed Magazine: magazine with original and reprinted stories
Daily Science Fiction: magazine with original stories, new every day!
Strange Horizons: magazine with original fiction and poetry.
Tor.com fiction: new fiction isn’t published as often as it is in the other ‘zines, but it’s usually excellent stuff.
Nature Futures: super short stories originally published in the scientific journal Nature.
Abyss & Apex: magazine of speculative fiction, including flash fiction and poetry.
Apex Publications Free Content: short fiction and whole novel sample chapters. Apex has “darker” science fiction and horror.
Apex Magazine: The magazine branch of Apex Publications, with some free science fiction, fantasy and horror.
Infinity Plus: their free fiction archive is no longer being updated, but it has a good collection SF reprints and originals.
Project Gutenberg Science Fiction Bookshelf: stories in the public domain, so mostly older works
Free Speculative Fiction Online: a great searchable database of free science fiction, indexed by author
And if you are looking for stories by a specific author, it’s usually worthwhile to check the author’s personal website too.