All smartphones include a surprisingly capable Web browser. Writing Web applications opens up the possibility of creating a single app that’s accessed over the Web via the browser. If you have expertise in creating Web applications, this method might be your best bet to create apps for multiple platforms, using one set of files. The languages of choice for Web apps are Hypertext Markup Language (HTML), Cascading Style Sheets (CSS), and JavaScript. Knowing these languages can make creating Web apps easier.