Why companies are flocking to HTML5

FORTUNE — Something in the last 18 months kicked the HTML5 adoption machine into overdrive. Maybe it was tech giants Apple and Microsoft joining hands and dubbing it the future of the web. Maybe it was Google’s launch of the Chrome Web Store, with its focus on HTML5, last December. Maybe it was the HTML5-friendly iPad’s meteoric sales. Whatever it was, a recent wave of consumer-facing web apps from Amazon, Box.net and LinkedIn confirm that this much-hyped language has business’ blessing.

HTML5 is the latest version of the Web’s bedrock markup language, HTML. But it has come to stand for much more than the average, slow-gestating technical standard. HTML5 is also shorthand for a set of features and capabilities intended to make web sites behave more like conventional desktop applications, incorporating video, complex interactions and data as well as greater compatibility with new devices like smartphones and tablets. In development since the early-2000s, HTML5 was rocketed into the mainstream in April last year when Apple (AAPL) boss Steve Jobs issued a public missive deriding Adobe’s (ADBE) Flash and anointing HTML5 as the web’s future. Now, companies are turning to it to cut down on costs that can soar when developing simultaneously for Apple’s iOS and Google’s (GOOG) Android as well as to circumvent the headaches of varying app stores.

Indeed, adoption has soared. A recent survey from video search engine MeFeedia showed that at least 69% of web video is now available for playback via HTML5. Last December, that number was 54%; in January 2010, months before the iPad became a hit, it was 10%. “Developers out there are getting better at supporting all of HTML5’s more critical features, which is why we’re seeing more publishers building the actual experiences they want using web technologies,” says Faruk Ates, a creative design and web consultant who worked at Apple for three years.

Amazon’s (AMZN) Cloud Reader made waves when it was announced a few weeks ago. While it has a polished user interface and offline reading capability, it’s still rough around the edges with limited web browser support and a lack of notable features Kindle e-reader users already take for granted, including text highlighting, notes and full-screen reading. Still, that hasn’t stopped user from kicking the tires. Amazon would not disclose numbers, but a spokesperson told Fortune that its Cloud Reader had the best first week of any Kindle app to date. The company says missing features will be folded into future updates.

LinkedIn (LNKD) and Box.net’s HTML5 apps, meanwhile, use the technology for different reasons. While Amazon’s Cloud Reader seems intent on becoming the primary web app for Kindle users, LinkedIn’s is merely supposed to complement apps developed for Android and iOS. In other words, users who don’t own either type of device will still get functionality that approximates the native app. Same goes for Box.net’s new web-based offering. Although the Palo Alto-based cloud storage provider uses some HTML5 coding in its main site, it didn’t fully embrace the Web technology until more recently thanks to a new wave of engineers. “We probably could have supported it a year ago,” says Box.net CEO Aaron Levie. He says HTML5’s increasingly powerful tools blur the lines between Web and cloud, desktop and client-like functionality.

That doesn’t mean the technology doesn’t face obstacles. HTML5 apps are often limited when compared with their native counterparts. In LinkedIn’s case, the feature sets are similar but the user interface is noticeably less flashy. Some mobile device’s assets, like the camera, remain off-limits to HTML5. “Generally, there are certain areas where native is going to do better for you, like media photos and pictures,” explains Joff Redfern, LinkedIn’s mobile product head. “It’s sometimes a little harder to get at via HTML5. Other areas, like say, ‘infinite lists’ that scroll with dates that continue on and on, are handled a lot more gracefully in native code.” Box.net’s Levie admits certain programming tasks are still difficult to achieve in HTML, like getting the iPhone and iPad’s built-in Safari browser to allow file uploads.

Another problem is distribution. Apple’s App Store and Google’s Android Marketplace are partly popular because they keep the barriers to entry low for native apps. Currently, there aren’t many equivalent web app stores besides Google’s fledgling Chrome app store. And, consumers don’t have an awareness of HTML5, the way they might of the Amazon, Apple or Google brands.

What’s certain is that HTML5 will likely play a pivotal role as companies position themselves vis-a-vis each others’ devices and marketplaces. It may take years before new HTML5 apps tackle more rigorous tasks that process lots of data, like video editing for instance. In the mean time, more and more major firms are likely to find the technology’s flexibility and low costs too tantalizing to resist.