Doctors, haircuts, even kittens -- now on demand, via your smartphone

October 29 was a typical workday for thousands of people in the US, except for one thing: a fuzzy kitten showed up on their desks.

They had 15 minutes to cuddle and snuggle with the purring furballs, thanks to a service offered by ride-sharing company Uber on National Cat Day.

"It's been a little over a week after #UberKITTENS and we are still recovering from the cuteness overload," Uber wrote in a blog post earlier this month after getting 30,000 requests for the kitten visits this year, the second time it offered the delivery service. "Everyone went catnip crazy and together we almost broke the Internet."

Welcome to the world of on-demand services, where everything from haircuts to snowplows to ice cream on a hot day and even beer and marijuana are a just a smartphone away. On-demand mobile apps are even reviving some traditions, like physicians' house calls, which faded into obscurity in the 1960s. Some companies offer services that defy categorization, like same-day weddings, skywriting and mariachi fiestas.

This delivery app boom marks the beginning of a shift in how busy people navigate today's modern world and feed into what Uber CEO Travis Kalanick has called the "give me what I want and give it to me now" attitude.

Here to stay?

On-demand doctors, beer and haircuts come as no surprise to John Morgan, a professor at UC Berkeley's Haas School of Business who studies online competition. He compares what's happening with on-demand services to the early days of eBay, which created an online marketplace for odd, interesting and desirable goods (like the Pez dispensers that eBay founder Pierre Omidyar's wife collected).

"People had a lot of junk lying around since time immemorial, but there was no real market for it," Morgan said. "eBay created an outlet where this stuff could be turned into cash and that remains a thriving business model."

On-demand services and apps are similar, Morgan said.

"Until recently, there was no market where you could turn these things into money," Morgan said. "Just like novelties and collectibles, there's no reason to think that demand for handy little programs will disappear any time in the foreseeable future."

Uber, which itself is an on-demand service that lets people hail rides with their smartphone, has come up with a steady stream of on-demand promotions over the past few years. Besides kittens, it's delivered Christmas trees, ice cream, barbecue and puppies. There have also been on-demand flu shots, Valentine's Day roses, mariachi fiestas and even skywriting. Other promos included same-day weddings and helicopters to the Hamptons. No stranger to controversy, Uber even promised to match riders with "sexy girl" drivers in France but nixed that particular promotion after allegations of sexism.

The idea behind initiatives like UberKittens is to explore the "platform's capabilities" and come up with "unique ways to surprise, delight and address the needs of riders," Uber spokeswoman Kristin Carvell said in an email.

Another component of Uber's wacky on-demand ideas is to partner with various companies and organizations. With UberKittens, for example, the kittens came from animal shelters and the ultimate goal was to get them adopted. Each 15-minute cuddle with an UberKitten cost $30 and those proceeds went to the shelters. During this year's National Cat Day, Uber said it raised more than $17,000 for participating shelters and 21 kittens were adopted.

Uber's on-demand promos also seem to be part of the company's plan to expand from ride-sharing to deliveries. Not only did Kalanick allude to that possibility at the Fortune Tech Brainstorm conference last year, but also the company reportedly hired the executive who was heading Google's same-day delivery service, Google Express, earlier this month.

While snuggling with kittens does have undeniable appeal, it's not likely to last, said Morgan. He believes apps must fill a need for them to have longevity.

"Many of the more silly or offensive ones will go the way of the dodo bird," Morgan said. "The UberKitten thing is kind of cute, but I think all it is, is cute."

House calls

Nabil Fanaian was hit with the flu at the worst time possible. En route to a work conference he became feverish, nauseated and chilled. By the time he checked into his hotel in Miami, Fanaian felt so weak he had to cancel all of his meetings.

"I'm in a hotel. I'm in a foreign city," Fanaian said. "I'm not about to get dressed and grab a cab to urgent care."

Instead, he pulled out his smartphone, tapped his Medicast app and asked for a doctor. The physician arrived within an hour, his black duffel bag equipped with everything from a stethoscope to blood pressure cuffs. One injection, a dose of prescription medicine and a $199 flat fee later, and Fanaian greeted the next morning feeling like new.

Medicast, with its on-demand doctors, is just one of many new services now bringing experts and professionals into people's homes and offices.

Take Shortcut, an app that dials up on-demand barbers. Irvin Slobodskaya desperately needed a haircut last year. But he had a problem: His busy job didn't let him slip out of the office during normal barbershop hours. Slobodskaya figured others had the same issue, so he came up with Shortcut -- which sends hairdressers to shaggy males across New York City all hours of the day. For $75 (prices drop as more people get cuts), a vetted barber will show up in about 30 minutes ready to trim hair and style beards.

"Shortcut was born out of necessity," Slobodskaya said. "The person we are looking for is someone who's primarily time-conscious with little wiggle room." What's more, an on-demand haircut provides a "more intimate experience than you'd get at the barbershop" since "you're inviting someone into your home."

Customers like Shortcut's convenience and simple, one-tap flat fee, Slobodskaya said.

It's the same for other on-demand apps.

Bannerman, an on-demand service for private security guards, launched last year. Initially, its CEO and founder, Johnny Chin, designed the app to give people safety and security at a moment's notice for $35 per hour. But "it's turned into convenience for people," he said. Now bars, offices, individuals, event planners and celebrities have begun hiring Bannerman security guards on the fly.

"We're in a culture where people want things right away," Chin said.

Joe Waltman and Brian Hur, co-founders of on-demand veterinary service VetPronto, are seeing the same trend. Waltman and Hur created VetPronto after spotting three main problems customers had with vet visits: endless hours in the waiting room, confusing billing and difficulty transporting pets to the office. After testing various solutions to these issues, like video consultations and a Q&A service, they decided an on-demand service with a flat fee of $129 per visit would be more convenient for clients and less stressful for pets.

While analysts, like Forrester and Gartner, are unclear on how big the on-demand market is and how fast it's growing, anecdotal evidence points to an upward swing. VetPronto, Shortcut, Bannerman, Medicast and many other on-demand app companies all said they're seeing their businesses quickly grow.

Steve Schlafman, a venture capitalist with RRE Ventures, has mapped out more than 70 on-demand startups. He wrote in a blog post in April that venture capitalists have "poured more than $1.75 billion" into these companies and he expects that number to increase.

"The 'uberification' of our economy signals a fundamental shift in the way that local services are discovered and fulfilled," Schlafman wrote.

Getting personal

When Fanaian was lying sick in his hotel room, he said he felt more of a personal connection with the physician than he might have had at a hospital. The doctor came in, placed his equipment on the nightstand, and gently had Fanaian sit up so he could put his stethoscope on his back and listen to him breathe. There was something caring about the experience. "It's a comfort factor," Fanaian said.

On-demand services are inherently modern. They take software, programmers, servers and smartphones. Yet something rather old-fashioned has emerged with this new service -- person-to-person experiences.

Dr. Sahba Ferdowsi, one of Medicast's co-founders and its chief medical officer, said his goals with the service are to bring "passionate care" back into medicine and have more patient engagement.

"What's really great is tech is at the core of what we do," Ferdowsi said, "but it doesn't come in the way."