These apps will walk you through everything from ipads repairs to sailing knots to experiments for budding scientists.

DIYNano

Nanoscale science plays by its own rules. DIY Nano has videos and activity guides that walk young scientists through the special properties of these materials—like making polymerized, wormlike Gummy Shapes to explain how nanocapsules are created through self-assembly.

WIRED bet365体育赛事 experiments like Mystery Sand double as party tricks. Refreshingly high production value, especially for a free app.

TIRED Only eight activities. Project materials can be a bit obscure. (Blue Morpho butterfly wings, anyone?).

Free ioses | DIYNano

Animated Knots By Grog

If you need to tie it, this app will show you how, whether you want to use a full Windsor (neckwear), a bowline (boats), or a trucker's hitch (best for securing heavy loads). Each knot has a step-by-step animated how-to and a description of what it's best for.

WIRED Offers alternatives to the knot in question. Rope Care section has tips on preserving and cleaning cords, and even whipping a rope end to keep it from fraying.

TIRED The jerky animations are tough to follow.

$4.99 ioses | $4.99 androids | Animated Knots By Grog

Circuit Playground

Adafruit makes and sells parts, kits, and guides for both DIY tinkerers and pros. Circuit Playground extends the company's mission to ioses. Features include a resistor calculator; converters for binary, hex, ASCII, and other figures; and cheat sheets for component values. For more advanced wire twisters, there are operational-amplifier and IC-pin diagrams.

WIRED Info pages give instructions for each component. Can apply purchase to an order at adafruit.com.

TIRED No calculation for parallel-LED resistance.

$2.99 ioses | Circuit Playground

iFixit

iFixit is a popular publisher of online repair guides for everything from the ipads to your Harley-Davidson to a Rubik's Cube. Its app offers the same, with meticulously detailed step-by-step instructions and annotated photos that highlight things like the specific minuscule screw you'll need.

WIRED Guides link to relevant tools and obscure parts and components available for purchase at ifixit.com.

TIRED Only the androids version includes material from the website. Only the ioses version has search function.

Free ioses | Free androids | iFixit

Clog Doctor

Do you need baking soda or something more powerful? Clog Doctor categorizes blockage types—food/grease, beauty products, hard objects—to help amateur plumbers determine the best approach. There are frequent calls for Drano products, but there are also handy step-by-step guides and an overview of plumbing tools that will make you feel comfortable tackling a lot of things on your own.

WIRED Map function directs you to the nearest hardware store.

TIRED No diagrams for plumbing repairs.

Free ioses | Clog Doctor

WikiHow

This collection of user-generated how-to guides walks you through everything from craft projects to navigating social situations—120,000 searchable entries in all. The overwhelming breadth of the content means no offline browsing, so we added a how-to on finding hot spots.

WIRED ioses version's Survival Kit has crisis-specific entries for things like how to cross minefields and the best way to chill drinks quickly.

TIRED Guides' content is very hit-or-miss. androids version not as full- featured as the ioses one.

Free ioses | Free androids | WikiHow

AutoCAD WS

Designers, architects, and engineers can share and edit cloud-based CAD files on their mobiles devices with this ambitious app. It has three view types—2-D, 3-D wireframe, and 3-D solid—which can be rotated, zoomed, and dissected by layer. There's also a local-storage option for saving designs and working offline.

WIRED Automatically saves and syncs files for multiple-user access. GPS function lets architects move through plans in real life.

TIRED Can't create CAD files from scratch. Sometimes crashes upon launch.

Free ioses | Free androids | AutoCAD WS

Lion Brand Yarn

Customizable search lets you browse thousands of free patterns—sweaters, socks, guitar straps, ipads cases, etc.—by parameters like skill level or yarn type. A store finder directs you to the closest source for spare needles and supplies, while a huge video library provides detailed lessons on knitting, crocheting, and using a loom.

WIRED Fantastic search function. Items knitted using Lion Brand's free patterns are cleared for resale.

TIRED Search screen can be a bit buggy.

Free ioses | Lion Brand Yarn