The tool that promises to launch the next era of websites, smartphone apps and online video is finally finished.HTML5, the long-in-the-works update to the language that powers the Web, is "feature complete," according to an announcement made Monday by the standards-setting Worldwide Web Consortium (W3C). There's still some testing to be done, and it hasn't yet become an official Web standard -- that will come in 2014. But there won't be any new features added to HTML5, which means Web designers and app makers now have a "stable target" for implementing it, W3C said.The HTML5 language lets developers deliver in-the-browser experiences that previously required standalone apps or additional software like Java, Adobe's (ADBE) Flash or Microsoft's (MSFT, Fortune 500) Silverlight. It supports lightning-fast video and geolocation services, offline tools and touch, among other bells and whistles.The W3C has been developing the spec for the better part of a decade."As of today, businesses know what they can rely on for HTML5 in the coming years," W3C CEO Jeff Jaffe said in a prepared statement. "Likewise, developers will know what skills to cultivate to reach smart phones, cars, televisions, e-books, digital signs, and devices not yet known."Most of the top browser makers didn't wait for the language to be 100% finished before building support for some elements into their software. The latest versions of Microsoft Internet Explorer, Google Chrome, Mozilla Firefox and Apple Safari are already compatible with most HTML5 elements.App developers followed suit.Netflix (NFLX) and Google's YouTube are two of the most prominent HTML5 adopters, but many others have also taken the leap. The Financial Times abandoned its smartphone app last year in favor of an HTML5 mobile website. The site looked and functioned like a native app -- with the advantage that FT didn't have to make changes to multiple versions of its code on multiple smartphone platforms. (Using a mobile website instead of a native app also let FT avoid paying Apple for in-app purchases.)Google (GOOG, Fortune 500), a strong supporter of HTML5, produced a viral interactive video in 2010 with the help of rock band Arcade Fire that showed off the potential of the new Web features. Firefox browser maker Mozilla made a splash in February when it created a smartphone operating system called "Boot to Gecko," which is almost entirely based in HTML 5.HTML5 grew prevalent enough by 2010 that then-Apple CEO Steve Jobs was able to unleash an epic rant against Flash and get away with it. A year later, Adobe more or less conceded that Jobs was right, abandoning its mobile Flash software in favor of HTML5 support. In November 2011 blog post, Adobe called HTML5 "the best solution for creating and deploying content in the browser across mobile platforms."There's still more work to be done. W3C said that about 63% of Web and app developers are actively using HTML5 to make their sites and software, but "browser fragmentation" remains a big reason why many still aren't using it. Though most up-to-date browsers support at least some aspects of HTML5, older versions of some Web browsers like Microsoft's (MSFT, Fortune 500) Internet Explorer don't.That's why W3C is working on cementing HTML5 as a new Web standard, making it interoperable and fully supported by any modern browser. It will take two years to complete the testing and standardization of HTML5, the consortium said.What's next? W3C is already working on HTML 5.1, the first parts of which were just submitted in draft form.