A man wakes up from a car crash to find that he is an "electric ant": an android programmed to believe it is human. At home he uses micro-tools to open up his own chest and discovers a tiny spool of tape inside. Punching new holes in the tape makes new objects appear in his world, obscuring a section makes the world disappear. The android cuts the tape, and hears a rushing wind as all reality is revealed to him.

The contradictory concepts at the heart of Philip K Dick's 1969 short story The Electric Ant have fascinated me ever since I first read it 20 years ago. It's the capacity of the science fiction story to get us thinking about intriguing concepts that gives the form its punch. Today, the short-story magazines that helped to popularise science fiction are all but gone. But a new generation of online magazines has taken their place, and is transforming the genre again.

Lightspeed magazine, under editor John Joseph Adams, has made a giant name for itself in recent years by publishing some of the very best science fiction in the field, with a roster of new and established talent including Seanan McGuire, Ted Chiang, Ramez Naam, Maureen F McHugh and Ken Liu. Lightspeed stories often blend the brain-candy high concepts that SF readers love with the kind of quirky humour that all geek culture adores. But there is also a dark edge and serious purpose to the sci-fi Lightspeed magazine showcases.

Since its founding in 2000 by Mary Anne Mohanraj, Strange Horizons has championed new writers in SF and broadened ideas of what the genre can achieve. Under editor-in-chief Niall Harrison the magazine has published some of the very best critical non-fiction writing about SF to be found online or off. If science fiction truly is, as the online magazine claims, "a vibrant and radical tradition of stories that can make us think … critique society … [and] offer alternatives to reality", then Strange Horizons has done more than any other publication in the 21st century to nurture that tradition.

Podcasts burst on to the short fiction scene in the mid-2000s and now even have their own awards, the Parsecs. Escape Pod is the best known, and has published many of sci-fi's best loved stories as audio productions. Sister publication Pseudopod is a great source of creepy horror stories, the warm, gravelly tones of host Alasdair Stuart raising him to near mythic status in sci-fi fandom. StarShipSofa's Tony C Smith is another contender for "voice of scifi" – maybe one day they'll go head to head?

But it is Tor.com that takes the crown as reigning champion of science-fiction magazines. With a team that includes the respected editors Ellen Datlow and Ann VanderMeer, its stories' subjects range from anthropological zombies to teenage hackers. The magazine has published many of the most exciting new talents, including Daniel José Older, Maria Dahvana Headley and Karin Tidbeck, alongside wide-ranging non-fiction content on everything from non-binary gender pronouns to re-reads of classic SF and fantasy books.

Sci-fi and fantasy's online success is down to the strength of its community. The genre's loyal fans mean that a new magazine such as Fireside can crowdfund more than $26,000 (£15,000) for its third year of publication. Fan support, too, a small fantasy fanzine such as Worlds Without Master with $1,540 an issue in patronage. If there's one lesson for writers and publishers to learn from the renaissance in sci-fi short fiction, it is that fans matter.