some more stories for the list:
Eliezer Yudkowsky's free online short stories
Not all of this is hard sci-fi, but most of it is.
Lots of free stories by Cory Doctorow, most notably Down and Out in the Magic Kingdom
These stories have varying degrees of hardness in the sci-fi
"After Life", by Simon Gordon
An awesome story about a Singularity started by an uploaded human mind. Reasonably hard sci-fi.
and here are some stories that don't qualify as hard sci-fi, that you might like anyway:
"I have no mouth and I must scream", by Harlan Ellison
A very nasty story. A standard example of a "hyperexistential disaster" caused by an Unfriendly AI. Technically not hard sci-fi.
"Postsingular", by Rudy Rucker
This novel provides a convenient introduction to several transhumanist concepts, though the plot itself seems to be deliberately anti-transhumanist.
"Understand", by Ted Chiang
An entertaining story about "hacking" the human mind. Demonstrates the risks of a dangerously selfish person being the first to succeed at this. not really "hard" sci-fi at all.
"I don't know, Timmy, being God is a big responsibility", by Sam Hughes
An interesting story about some of the unexpected anthropic dangers of simulating entire universes, with an "infinitely powerful" computer.
"They're Made Out Of Meat", by Terry Bisson
An amusing short story illustrating the silliness of "carbon chauvinism"
that story about the clinic seed, by Keith Henson, Part 1 Part 2 Part 3 Part 4
A story about what might happen to primitive human cultures, after the Singularity.
Only some of these stories qualify as hard sci-fi
Oh, and of course there's the massive collection of sci-fi stories in the Baen Free Library. I haven't even begun reading through this yet.
"that story about the clinic seed" gets my recommendation, "I don't know, Timmy, being God is a big responsibility" is fun, as is "They're Made Out of Meat", but my favorites have to be Doctorow's stuff. "Rapture of the Nerds" gets incredibly Posthumanistic at points.
Transhumanism and Hard Sci-fi category at FictionPress.com
Lots and lots of sci-fi at FictionPress in general (no hardness guarantees made)
My sci-fi short stories, in varying degrees of hardness and in two categories. (T) marks significant transhumanist themes.
Fragments of frozen time:
Childhood's End Even after nine years, people still stare at us.
Cthulhupunk With his mad, half-unseeing eyes, Calinob Dis stared into the eternity.
In a Billion Years Their embrace is wordless, simultaneously physical and mental. (T)
The Chamber of Sounds I stand here, in my small closet, locked away from all other life.
To Live and Die for the God-Emperor The party in the Menovian asteroid belt has been going on non-stop for ten millennia now.
Stories:
Colonization Humanity is standing at a crossroads, at a time when the galaxy still remains ready for the taking.
Cryoshift A rebirth. (T)
Union Two lovers, machine-mediated telepathy, and the consequences. (T)
The Ware Tetralogy: Free SciFi Download
Between 1982 and 2000, Rudy Rucker wrote a series of four sci-fi novels that formed The Ware Tetralogy. The first two books in the series – Software and Wetware – won the Philip K. Dick Award for best novel. Later Freeware and Realware followed. This summer, Prime Books republished the tetralogy in one big volume, complete with an introduction by William Gibson that calls Rucker “a natural-born American street surrealist” or, more simply, one sui generis dude. And now the even better part: Rucker (who happens to be the great-great-great-grandson of Hegel) has released The Ware Tetralogy under a Creative Commons license, and you can download the full text for free in PDF and RTF formats. In total, the collection runs 800+ pages. For more information on the book and the free download, visit here. And don’t forget to donate to the Creative Commons Legion of Superheroes fundraising campaign.
Here's one of mine:
Not actually fan fiction, but inspired by two existing works many readers will recognize.
Does Schlock Mercenary count as Hard Scifi? What about Freefall? They've both got FTL travel, and the former has other fairly miraculous technologies (like the matter annihilation plants and artificial gravity systems intimately related to them), but they're well thought out with the rational implications of them seen and discussed.
I deleted one of the links. I mistakenly copied it from another list. Just delete the story by Ian R MacLeod if you've saved it.
I posted a link to this on reddit/r/scifi, reddit brought back this list in return:
Hannu Rajaniemi -Elegy for a young elk
This may have some good stuff, not read it yet.
Blindsight, Peter Watts
Eighty years in the future, Earth becomes aware of an alien presence when thousands of micro-satellites surveil the Earth; through good luck, the incoming alien vessel is detected, and the ship Theseus, with its artificial intelligence captain and crew of five, are sent out to engage in first contact with the huge alien vessel called Rorschach. As they explore the vessel and attempt to analyze it and its inhabitants, the narrator considers his life and strives to understand himself and ponders the nature of intelligence and consciousness, their utility, and what an alien mind might be like. Eventually the crew realizes that they are greatly outmatched by the vessel and its unconscious but extremely capable inhabitants.
When the level of this threat becomes clear, Theseus runs a kamikaze mission using its antimatter as a payload, while Siri returns to Earth, which, as he grows nearer, it is apparent has been overrun by vampires. Non-sapient creatures are beginning to exterminate what may be the only bright spark on consciousness in the universe.
Ventus, Karl Schroeder
Ventus is well-written and fun, as well as having IME the most realistic treatment of nanotech I've yet encountered in SF. Schroeder is definitely an author to watch (this is his first novel). The setup is that some agents from the local galactic civilization have come to an off-limits world hunting a powerful cyborg who may be carrying the last copy of an extremely dangerous AI god. The tough part is that the world is off-limits because the nanotech on that world is controlled by AIs that destroy all technology not made by them, and aren't terribly human-friendly.
Crisis in Zefra, Karl Schroeder
In spring 2005, the Directorate of Land Strategic Concepts of National Defense Canada (that is to say, the army) hired me to write a dramatized future military scenario. The book-length work, Crisis in Zefra, was set in a mythical African city-state, about 20 years in the future, and concerned a group of Canadian peacekeepers who are trying to ready the city for its first democratic vote while fighting an insurgency. The project ran to 27,000 words and was published by the army as a bound paperback book.
Accelerando, Charles Stross
The first three stories follow the character of "venture altruist" Manfred Macx starting in the early 21st century, the second three stories follow his daughter Amber, and the final three focus largely on her son Sirhan in the completely transformed world at the end of the century.
In Accelerando, the planets of the solar system are dismantled to form a Matrioshka brain, a vast computational device inhabited by minds inconceivably more complex than naturally evolved intelligences such as human beings. This proves to be a normal stage in the life cycle of an inhabited solar system; the galaxies are filled with Matrioshka brains. Intelligent consciousnesses outside of Matrioshka brains may communicate via wormhole networks.
The notion that the universe is dominated by a communications network of superintelligences bears comparison with Olaf Stapledon's early science-fiction novel Star Maker (1937), although Stapledon's advanced civilizations communicate psychically rather than informatically.
The Lifecycle of Software Objects, Ted Chiang
A triumphant combination of the rigorous extrapolation of artificial intelligence and artificial life, two of the high concepts of contemporary SF, with an exploration of its consequences for the ordinary people whose lives it derails. Ana Alvarado is a former zookeeper turned software tester. When Blue Gamma offers her a job as animal trainer for their digients--digital entities, spawned by genetic algorithms to provide pets for players in the future virtual reality of Data Earth--she discovers an unexpected affinity for her charges. So does Derek Brooks, an animator who designs digient body parts. The market for digients develops and expands, cools and declines after the pattern of the software industry. Meanwhile Ana, Derek, and their friends become increasingly attached to their cute and talkative charges, who are neither pets nor children but something wholly new. But as Blue Gamma goes bust and Data Earth itself fades into obsolescence, Ana and the remaining digient keepers face a series of increasingly unpleasant dilemmas, their worries sharpened by their charges' growing awareness of the world beyond their pocket universe, and the steady unwinding of their own lives and relationships into middle-aged regrets for lost opportunities. Keeping to the constraints of a novella while working on a scale of years is a harsh challenge. Chiang's prose is sparse and austere throughout, relying on hints and nudges to provide context. At times, the narrative teeters on the edge of arid didacticism; there are enough ideas to fill a lesser author's trilogy, but much of the background is present only by implication, forcing the reader to work to fill in the blanks. (Indeed, this story may be impenetrable to readers who aren't at least passingly familiar with computers, the Internet, and virtual worlds such as Second Life.)
The Island, Peter Watts
"The Island" is a standalone novelette. It is also one episode in a projected series of connected tales (a lá Stross's Accellerando or Bradbury's The Martian Chronicles) that start about a hundred years from now and extends unto the very end of time. And in some parallel universe where I not only get a foothold into the gaming industry but actually keep one, it is a mission level for what would be, in my opinion, an extremely kick-ass computer game.
The Things, Peter Watts
Divided by Infinity, Robert Charles Wilson
In the year after Lorraine's death I contemplated suicide six times. Contemplated it seriously, I mean: six times sat with the fat bottle of Clonazepam within reaching distance, six times failed to reach for it, betrayed by some instinct for life or disgusted by my own weakness.
I can't say I wish I had succeeded, because in all likelihood I did succeed, on each and every occasion. Six deaths. No, not just six. An infinite number.
Times six.
There are greater and lesser infinities.
But I didn't know that then.
Crystal Nights, Greg Egan
The Finale of the Ultimate Meta Mega Crossover
Vernor Vinge x Greg Egan crackfic.
Concepts contained in this story may cause SAN Checking in any mind not inherently stable at the third level of stress. Story may cause extreme existential confusion. Story is insane. The author recommends that anyone reading this story sign up with Alcor or the Cryonics Institute to have their brain preserved after death for later revival under controlled conditions. Readers not already familiar with this author should be warned that he is not bluffing.
A story to illustrate some points on naturalistic metaethics and diverse other issues of rational conduct.
Features Baby-Eating Aliens.