How does 3D printing even work? What's all this about 3D-printed guns? Can you 3D-print a 3D printer? Why are they so expensive? What can you actually make with them? Apart from guns...The ethical and legal questions around 3D printing and firearms are important and complex, but they also tend to hoover up a lot of the mainstream media attention for this area of technology. But it's the "what can you actually make with them" question that's been pulling me in recently.There's a growing community – from individual makers to nascent businesses – exploring the potential of 3D printing. This feature is just a snapshot of some of the products and projects that caught my attention, rather than a definitive roundup.A taste of what's happening, but one that's ripe for your comments pointing out better examples in these categories, and other areas that have been left out. All contributions are welcome, but here are 30 things to start the discussion off.1. RAF Tornado fighter jet partsEarly this year, BAE Systems said that British fighter jets had flown with the first time with components made using 3D printing technology. Its engineers are making parts for four squadrons of Tornado GR4 aircraft, with the aim of saving £1.2m of maintenance and service costs over the next four years. "You are suddenly not fixed in terms of where you have to manufacture these things," said BAE's Mike Murray. "You can manufacture the products at whatever base you want, providing you can get a machine there."2. Arms for childrenTime's article from earlier this month on the work of Not Impossible Labs makes for powerful reading: a project using 3D printers to make low-cost prosthetic limbs for amputees, including Sudanese bomb-blast victim Daniel Omar. But this is just one of the stories emerging: see also 3Ders' piece on a four-year old called Hannah, with a condition called arthrogryposis that limits her ability to lift her arms unaided, but who now has a Wilmington Robotic Exoskeleton (WREX for short) to help, made using 3D printing.3. Old Trafford and the Etihad StadiumManchester-based company Hobs' business is based around working with architects, engineers and other creatives to use 3D printing as part of their work, but to show off its capabilities, the company 3D printed models of the city's two football stadia – Old Trafford and the Etihad Stadium – giving them away in a competition for Manchester Evening News readers. The models were estimated to be worth £1,000 each.4. Unborn babiesNot actually as creepy as it sounds. This is more an extension of the 4D ultrasound images of babies in the womb that have become more popular in recent years. The theory: why not print them out? One company doing it, 3D Babies, didn't have much luck with a crowdfunding campaign last year, raising $1,225 of its $15,000 goal. Even so, its website is up and running, offering eight-inch "custom lifesize baby" models for $800 a pop.5. Super Bowl shoe cleatsExpect to see a number of big brands launching 3D printing projects this year – part R&D and part PR campaigns. Nike is one example: it's showing off a training shoe called the Vapor Carbon Elite Cleat for this year's Super Bowl, with a 3D-printed nylon base and cleats – the latter based on the existing Vapor Laser Talon, which was unveiled a year ago.6. Honda concept carsAdmittedly, not an actual concept car that you can drive. Not yet. But Honda has made five 3D-printable models available from its website for fans to download and make, including 1994's FSR Concept and 2003's Kiwami. So it's more about shining a light on the company's archives and being seen to be innovative – although the potential of 3D printing for internal prototyping at all kinds of manufacturers (cars included) is one of the most interesting areas for 3D printing.7. Lost statues in AfghanistanIndustry site 3D Printer tells the tale of the Buddhas of Bamiyan, two of the largest standing Buddha statues in the world, which were destroyed by the Taliban in 2001 after five centuries watching over the surrounding landscape. A team of experts is now trying to put them back together, with 3D printing used to make 1/25 scale models as part of the planning process.8. Wheelchair rampsRaul Krauthausen is the man behind Wheelmap, a crowdsourced map of wheelchair-friendly places around the world. In December last year, though, he published the details of his experiments with a MakerBot 3D printer to create his own mini wheelchair ramp. "Of course, there is still room for improvement. For example, I cannot reach the ramps in the back pocket and set them down by myself. But that was not really the idea. I find asking for help acceptable," he wrote.9. Skin'n'bones3D printing tissue could be an article in itself, and I'd welcome your suggestions of innovation happening in this specialised area. The piece that caught my attention was on KVUE about the work of a research team at the University of Texas in El Paso to print skin and other tissue. "Something maybe out of a science fiction book, but now it’s a reality," as one member of the team put it. But from the BioPen that 'draws' cells onto patients through to 3D bio printers that could one day be producing organs, this is an area of intense activity in 2014.10. SelfiesYeah, selfies. As if flooding Instagram with shots of yourself wasn't enough, 3D printing is being used by a number of companies to produce essentially action figures of the people printing them out, rather than the standard superheroes, cartoon brands and so on. Cubify's 3DMe got plenty of attention at the CES show earlier this month for its 3D-printed figurines, but from bobble heads to putting yourself on your own wedding cake, there's seemingly no end to this 3D-printing subcategory.11. Book slipcasesMakerBot brought us the story of Chang-rae Lee's latest novel On Such a Full Sea, which has a limited-edition version with a 3D-printed slipcase designed by her publisher's art director Helen Yentus. She said that the idea was to give people "the opportunity to have something to hold onto that is not available in digital form", with Lee adding that "it revisits the book as an object... the pleasure I get from reading is something tactile".12. Houses3D-printed houses aren't such a big leap, conceptually, from some of the developments in construction and pre-fabricated homes over recent decades. Even so, some of the projects out there in the wild are fascinating. A team from the University of Southern California is working on a machine that is "basically scaling up 3D printing to the scale of building" by squirting out concrete in layers, while in Amsterdam, a 20-foot 3D printer called KamerMaker is printing a house as an artwork.13. Duck legs and horse shoesIt's not just humans who are getting a 3D-printed helping hand (or arm, or leg...) – animals are also on the agenda. Witness TechCrunch's Designers Delay Duck's Death With 3D-Printed Limb story, about a duck called Dudley who lost his leg in an "aggressive chicken fight" and now has a 3D-printed replacement. Or look at a horse named Holly's 3D-printed titanium shoes, built by CSIRO to help her recover from a painful disease called Laminitis.14. Toys from children's appsChildren making their own toys (or, more accurately, customising them) via 3D printing is a growing area of experimentation. British startup MakieLabs was early into the trend: its Makies Doll Factory iPad app helps kids create a doll, which their parents can then order. But then there are apps like Blokify – essentially the creative sandbox part of Minecraft with the option to 3D-print the things children build at home, or order them from partners. On the way is Monstermatic, a mobile game where children create monsters, and can then print them. All this is expensive right now, but it's early days.15. Crime scenesVice's headline tells the story neatly: 3D-Printed Crime Scenes Are Coming to a Courtroom Near You. Although in truth, unless you live in New Mexico, they may not be that near you for a while. A police station in Roswell has apparently bought a 3D scanner in order to create graphical representations of crime scenes to complement standard photography.16. Music boxesA startup called Left Field Labs has shown off customisable music boxes, with the twist being that you can print out the music on your own 3D printer, and order the box to play it on. What's more, you compose the tune using a simple grid-based system online. For now, the company isn't taking new orders for prints, but it's letting people save their creations for when it reopens them.17. WindpipesAnother biological application that's in its early days: a doctor in New York whose team is working on 3D silicone tracheas which take 15 minutes to 3D-print. It's some way off actually being used for patients, mind. "We have made a 3D airway. The next step is then to incorporate or embed stem cells within that that will differentiate into cartilage, which is the bulk of what the trachea is made up of..."18. Hubble Space Telescope imagesThere are some beautiful images coming back from the Hubble Space Telescope, but blind people can't see them. Or can they? NASA reported this month on the project of two astronomers at the Space Telecope Science Institute who are turning Hubble images into 3D-printed pictures with stars, filaments, gas and dust. "I want to represent that in 3-D and have people feel it with their fingers because they can't see it. They would be able to spatially understand where important features are relative to everything else and what the structure is," they explained.19. JewelleryIn the run-up to Valentine's Day, expect to read a blizzard of stories about 3D-printed rings, necklaces and other jewellery. From American Pearl's wedding rings ("thousands of possibilities, billions of permutations: every piece is like a snowflake") to MIT-born startup Matter.io's design-your-own-bling service to the work of individual designers like Maria Jennifer Carew there is plenty happening on this front.20. SoilNow back down to earth: as in actual earth. A team at Abertay University is working on creating 3D-printed models of the structure of soil, in order to understand their pores and "the ways in which the fungi and bacteria living within them interact" in Phys.org's words. "By inserting microorganisms (such as fungi and bacteria) into the pore spaces within the plastic soil, the scientists can now observe how these microorganisms move through it, survive, find food sources and interact."21. Inflatable flowersSomething else for Valentine's Day perhaps: 3D-printed inflatable flowers. Designed by Richard Clarkson, they're part of an experiment to produce the world's first inflatable 3D print. "Forcing air into the cavities of the print causes it to ‘bloom’ and thereby reveal the complexity of its physical structure," explains his website. So, not a product as such, but a glimpse at "an opportunity to generate complex forms and dynamic structures that are impossible to make by any other means".22. Iceberg holiday resortsThe idea of holidaying on an iceberg may not appeal – no Titanic jokes, please – but two students at the Pratt Institute School of Architecture used 3D printing to flesh out their idea for floating iceberg resorts, complete with internal hot springs. "The way Andrew and I were able to be more confident in pursuing this project was having a way to build it," said one of the pair. "I can’t see myself not having a 3D printer in the future; I think it’s just going to be part of what I do for the rest of my life," said the other.23. Chocolate and other foods3D-printed food is regularly in the news, with one of the hits of this year's CES show being the ChefJet 3D printer, which uses sugar and cocoa butter rather than plastics to create various sweet treats. The company behind it, 3D Systems, is also working with confectionery brand Hershey's for some experiments. But as this handy wrap-up by Business Week makes clear, pizza, ravioli and chickpea nuggets are also on the 3D printing menu.24. MenurkeysThe story of 10 year-old Asher Weintraub was heartwarming last year: he created something called a Menurkey – a cross between the menorah candleabra and a turkey – which raised nearly $50k on Kickstarter to become a product. The initial prototyping was done with a 3D printer at MakerBot's headquarters, although the company noted that Asher was keen to get himself a model to work on future products.25. InsolesAs things to fling $1.75m of funding at, a startup expected "to make 3D-printed shoe insoles both sexy and mainstream" sounds like quite a gamble. Still, that's the intention of SOLS, which announced its seed funding this week. Its customised 3D-printed insoles are aimed at making a range of shoes more comfortable. "It’s 2014. The idea that we buy the shoes that don’t fit is ridiculous..."26. Monkey handbagsThis comes from a Belgian company called Kipling, which is launching a 3D-printed handbag called The Monkey Madness City Jungle Shopper. Inspired by The Jungle Book, all bar the logo and handle are 3D-printed, with the video below providing a taster.27. BikinisYes, alright, an easy headline: turning any new technology into lingerie tends to get plenty of attention. Such was the case with the N12 from Continuum, made out of Nylon 12 with its parts "made directly by 3D printing and snap together without any sewing... For a bikini, the nylon is beautifully functional because it is waterproof and remarkably comfortable when wet." It's part of a wider range of fashion from the company, including a line of 3D-printed shoes.28. GuitarsDesigner Olaf Diegel isn't just making 3D-printed guitars: he promises to collaborate with the buyers to tailor the instruments to their musical and/or visual needs. His Spider design is particularly fun, coming from "the interpretation of the ultimate heavy metal instrument through the lens of arachnids". Diegel will even 3D-print musician or band names on the back of an instrument.29. Vinyl recordsMore music: Bloc Party's Kele Okereke was part of a project last December to release a new song as a 3D-printed record, sold from a pop-up shop in London as part of a charitable fundraising campaign. The actual record was made using a technique developed by American researcher Amanda Ghassaei for converting digital music files into 3D-printable records with wider, deeper grooves than traditional vinyl.30. Sad KeanuEven memes are getting 3D-printed in 2014. The collection of sullen Keanu Reeves models is the work of Japanese company idk: "a remarkable instance of 3D mini ennui moving to the mass market," (theguardian.com)ANN.Az