The mobile-apps industry is still in its infancy, but it is already taking on giants.

Apps are cheap to make and easy to distribute, forcing many old-line industries to rethink the way they do business.

With a single click, millions of Americans are comparing prices, hailing taxis and downloading addictive videogames to their smartphones.

'You don't have to be a huge company with billions of dollars to build a business anymore; you really can be two guys in a basement,' said Jeff Haynie, chief executive of Appcelerator, which licenses software for app developers. 'Very traditional models are getting disrupted.'

That trend is set to continue as more consumers switch from simple mobile phones to smartphones that spur app consumption. Last year marked the first time more U.S. mobile phone users had smartphones than simpler feature phones, according to data from comScore Inc.

Here are industries under pressure because of the rise of apps:

Amazon.com Inc. solidified the concept of 'showrooming' in 2011 when it introduced its Price Check mobile app, which allows people to compare store prices with online prices by pointing their smartphone at a barcode.

It has since become a phenomenon, as more consumers use big-box retailers and other stores to test out products, only to buy them cheaper online or directly from their phones.

Other such apps have followed, such as PriceScan and eBay Inc.'s RedLaser. The free apps have become more sophisticated, including directing users to nearby stores with lower prices and offering coupons and other rebates.

At Best Buy Co., more than three in five consumers now use their smartphone to comparison shop, up from about one in 10 two years ago, according to a recent survey from consulting firm Kurt Salmon Associates.

Retailers are trying various approaches to thwart showrooming, including stockingexclusive items, dynamic pricing schemes and price-matching.

Brookstone Inc. Chief Executive Stephen Bebis says the company was forced to change strategy by app users. Brookstone, known for its electronics products, has increased the number of house-branded and exclusive products to prevent itself from becoming a showroom for lower-priced e-commerce retailers, for instance.

'Sixty-five percent of our sales are now our own products,' said Mr. Bebis. 'I'm not sure there would be a Brookstone today if we hadn't done that.'

Apps for sharing and arranging rides have thrown a wrench into the engines of traditional black car and yellow cab services, which are an $11 billion industry.

With names like Lyft, SideCar and Uber, the apps promise cheaper and more efficient service by connecting drivers with passengers using Global Positioning Systems embedded in most smartphones.

The free-to-download services work differently. SideCar and Lyft rely on drivers who use their own cars to shuttle customers around town after work, on weekends and, in some cases, as a second job. Uber and the smaller TaxiMagic work with existing taxi fleets and function more like a traditional dispatcher, though with fares that can run higher.

The apps companies have faced regulatory pushback, including from the California Public Utilities Commission, which said the apps skirt taxi and limousine rules. The CPUC is reviewing the companies' business practices, while Philadelphia's Parking Authority has issued fines to SideCar.

While the services generally operate in just a few U.S. cities, they are expanding rapidly. Lyft started service in the Los Angeles area this year and will soon bring it to Seattle, while Uber recently began operating in Singapore, adding to locales in the U.S., Europe and Australia. SideCar this year is adding various U.S. cities such as Boston and Washington.

The rise of apps has caught the $15 billion U.S. videogame industry flatfooted.

The industry grew up selling game consoles and cartridges for people to use in their living rooms and basements, tethered to a television. And while videogames are also played on desktop computers and portable consoles, most game publishers were slow to embrace the small screen of the mobile phone.

New mobile games like the popular 'Angry Birds' and 'Cut the Rope' are low cost, typically 99 cents to download, or free with advertising support. Users could carry dozens of games with them on their smartphones and not face the added costs of buying new cartridges or CDs.

These businesses don't require the infrastructure that traditional game companies need, such as retail space for cartridges and consoles, as well as the cost of packaging,

Consoles typically cost $200 or more, and many shrink-wrapped video games cost $60.

Last year, packaged games sold in the U.S. totaled $7.1 billion in sales, down 21% from a year ago, while spending on purely digital content such as mobile games and in-app purchases jumped 16% to $5.92 billion, according to market researcher NPD Group.

Even new game makers like Zynga Inc. have been tripped up by the apps trend. Zynga rose to prominence by offering social games like 'FarmVille' on Facebook Inc.'s website. But Zynga's shares have plunged over concerns the company was overdependent on Facebook and was weak in mobile games.

'Zynga has always been aware of the power of mobile,' said Travis Boatman, Zynga's senior vice president of mobile. But 'the size and speed of the mobile business has been tremendous, more than anyone expected.'

A number of texting and free- or low-cost calling apps--notably WhatsApp and Skype