Appy days? Finding the future of the ubiquitous app
Apps. Without them, a smartphone is only a mobile - or the Apple Watch, just a humble wristwatch.
Apple's App Store, boasting more than 1.5 million apps, has topped 100 billion downloads. Android's Google Play lags slightly at 50 billion, but downloads there are ticking over faster - 70% more than Apple's in the first months of 2015.
The App Store, though, prevails in revenue, again by 70%. (Android's lead is largely in the developing world.) Both are growing hand over fist.
A revamped app store was a chief priority for Microsoft in designing the new Windows 10.
No decently dressed business now dares venture into the world without an app, with 61% of US adults, and around three quarters of Brits, carrying smartphones in their pockets.
App usage increased 76% last year, says research firm Flurry, with shopping, productivity, and messaging apps growing most of all.
"2014 was the first year where, at least in America, people spent more time on mobile apps than on the desktop and mobile web combined," says Itai Tsiddon, whose company Lightricks developed the apps Facetune and Enlight.
If this is the future of the internet, what does the future hold for the app?
A sprinkling of innovation from the likes of Uber and Airbnb has changed our expectations. It has prompted ripples of imitation, especially in their use of smartphones' sensor and location data, or Airbnb's peer-to-peer market for excess capacity.
"It's the Uber of things phenomenon," says Jyoti Bansal, chief executive of AppDynamics.
"There's now an Uber for this and for that - even an Uber for massage."
Uber wouldn't work as a desktop application.
But the titans of the internet are princes too of the app jungle.
Four of the five most-downloaded apps in the UK, including WhatsApp and Instagram, are owned by Facebook, according to analysis firm App Annie. And the fifth, YouTube, is the property of Google.
With so many out there, including over a million apps on Google Play, how can developers and users navigate them?
"With Google search responses coming within 250 milliseconds, our expectations as customers are increasing, so performance becomes more and more critical," says John Rakowski of AppDynamics.
The company is one of a growing number of start-ups orientated towards helping developers monitor app performance, and keep tabs on how it's doing in the wild.
Crucial fractions of seconds might be lost by not adapting to patchy network speeds, relying on laggardly third-party cloud providers, or overdoing time-intensive database calls, he says.
App stores also have limitations for both developers and downloaders.
Outside the top lists in each category, there is a mushrooming number of "zombie apps", which are effectively invisible to consumers - 83% per cent, by the end of last year - vying to get noticed or downloaded.
"We will start to see deluges of adverts for apps. We're now seeing television slots, billboards - this is all new, in the last year or so," says Simon Kendall from Adjust, an app analytics start-up based in Berlin.
Money spent on mobile advertising has recently caught up with the amount of time people devote to their mobiles, says Mr Tsiddon, though research spending has not, he says.
There also is increased willingness to pay for apps.
"When we launched Facetune," says Mr Tsiddon, "almost every app was selling for 99 cents; nowadays, we have moved our prices up to four to six dollars."
Meanwhile, companies increasingly find themselves interlacing nifty front end applications with legacy back-end core technology, says Brandon Bichler, from the London management consultancy firm Elixirr.
There also is a trend towards apps integrating different sorts of information, like Waze, which in 2012 began combining petrol prices with its navigation app to help users decide where to refuel.
Another trend comes from increasingly strict EU data-protection regulations.
The result may be a race to the top in data protection, predicts Mr Kendall, with new regulations making developers question "what sort of data are we mining, and is it creepier than it needs to be?"
When the killer app arrives for the smart watch and other new wearables, what will it look like?
"You don't just experience computing when you sit at your desk," notes Google engineering director David Singleton, who leads Google's development of its Android platform for smartwatches and wearables, Android Wear.
And we will soon experience it through apps increasingly appearing on televisions and also car dashboards, he adds.
He sees new gestures taking root in apps for wearables, such as scrolling by motion of the wrist.
And much being made of location - bringing up recipe apps when you are in a supermarket for example.
As well as their constant presence - quietly tracking how much you walk, and knowing (and tallying) if you are running, cycling, or doing press-ups.
"I think there's a huge trend here for apps to be able to plug into a user's context," says Mr Singleton.
This includes linking into the internet of things, telling a home automation system you are near, to turn your heating on say.
In the world of payments, this could mean "throwing what you want into a bag, walking out the door, and paying automatically," says Mr Bichler.
One challenge from smaller screens will be fiercer jostling by apps for your attention.
And perhaps even more than with smartphones, a second challenge for wearable apps is extending battery life.
What makes a good app?
Maciek Drejak, behind the Sleep Cycle alarm clock app and chief executive of Northcube, suggests the key lies in bringing "fun, simplicity, and value" to users, without being invasive or forcing them to learn new habits".
Omer Perchik, chief executive of the task-managing app Any.do, notes major trends towards messaging, as well as more action-orientated car, food, and hospitality apps.
"The interesting part would be if and how these two trends would merge," he says.
Agreeing on the importance of simplicity and seamlessness, Mr Bansal suggests a good app is intuitive, quick, and requires few clicks to achieve a task.
And Facetune's Mr Tsiddon praises apps with "no shady monetarisation mechanisms, just old-fashioned people with PhDs making straight-edge, quality software, and selling it".
A wrist-summoned Uber massage, then, from a person with a PhD? Maybe not yet.
But if it's a drink-dialing blocker you're after (Drunk Dial No!, 99 cents), games for your cat (Game for Cats, $1.99), or a pointless button (Pointless Button, free) — well, there is an app for that.