You could start with 'A Sound of Thunder' by Ray Bradbury. It shows the consequences of time travel in a very vivid way. 'Surface Tension' by James Blish is also a great choice. It tells a story about microscopic life forms and their struggle for survival, which is presented in a very sci - fi way.
Many libraries now have digital collections. You can access their online platforms and search for short sci - fi stories that are available for free borrowing. Additionally, platforms like Smashwords sometimes have free short sci - fi stories. You just need to search through their categories to find the ones you like.
I would recommend 'The Last Question' by Isaac Asimov. It's a classic that explores deep concepts about the universe and the future of humanity in a relatively short space. Another great one is 'All You Zombies' by Robert A. Heinlein. It has a mind - bending time - travel plot. And 'A Martian Odyssey' by Stanley G. Weinbaum is also very good. It offers a fascinating look at what life on Mars might be like.
One great collection is 'The Martian Chronicles' by Ray Bradbury. It has a series of short stories set on Mars that explore themes like human colonization and the encounter with the alien environment. Another is 'I, Robot' by Isaac Asimov. It contains short stories about robots and their relationship with humans, introducing his famous Three Laws of Robotics. And 'Nine Tomorrows' by Asimov as well, which offers a variety of thought - provoking sci - fi concepts in short story form.
Great sci fi short stories usually have a strong concept at their core. Like in 'Flowers for Algernon', the concept of intelligence and what it means to be human is central. They also tend to use science - fictional elements to enhance the story rather than just for show. In 'The Veldt', the virtual reality aspect serves to comment on family and society. Moreover, they can often be thought - provoking, making the reader consider different perspectives on topics such as ethics in 'I Have No Mouth, and I Must Scream' or equality in 'Harrison Bergeron'.
I would recommend 'The Time Machine' also by H.G. Wells. It's a short but very impactful story that explores time travel in an interesting way. It can be easily found for free. And then there's 'Flatland: A Romance of Many Dimensions' by Edwin A. Abbott. This unique story about different dimensions is both educational and fascinating.
For fantasy, you could check out 'Goblin Market' by Christina Rossetti. It has elements of the fantastical with the goblin merchants. In sci - fi, 'A Sound of Thunder' by Ray Bradbury is excellent. It shows how small changes in the past can have huge impacts on the future. Also, Neil Gaiman's 'How to Talk to Girls at Parties' is a fun and strange fantasy short story that blends the ordinary with the extraordinary.
One popular free sci - fi short story is 'The Cold Equations' by Tom Godwin. It's a thought - provoking story about a spaceship's pilot facing a difficult moral dilemma. Another is 'Flowers for Algernon' by Daniel Keyes, which, while often considered in the realm of science - fiction related to intelligence, is freely available in short - story form in many places and is quite well - known.
Richard Matheson's 'I Am Legend' is another excellent one. It's about a man who seems to be the last human alive in a world overrun by vampires. It has been made into movies multiple times, but the original story is a great piece of free sci - fi horror literature that explores themes of isolation, survival, and what it means to be human.
One great real sci - fi story is 'The War of the Worlds' by H.G. Wells. It tells the story of a Martian invasion of Earth, which was quite revolutionary at the time. Another is '2001: A Space Odyssey' by Arthur C. Clarke. It explores human evolution and the relationship with advanced technology through the journey of the spaceship Discovery. And 'Fahrenheit 451' by Ray Bradbury is also a significant one. It depicts a future society where books are burned and the importance of knowledge and free thinking.
Some well - known sci fi fiction stories include 'Ender's Game' by Orson Scott Card. It tells the story of a young boy trained in military strategy for a war against an alien race. The story delves deep into themes of morality, leadership, and the nature of the enemy. 'Brave New World' by Aldous Huxley is another. It presents a future society where people are genetically engineered and conditioned from birth to fit into a specific social class. It makes you think about the price of a seemingly perfect but soulless society.