WhatsApp has conquered the world of low-cost SMS alternatives, at least in the international market. The company's practically free system, which uses standard phone numbers and a text message-style interface, gained hundreds of millions of users before being acquired by Facebook for an amazing $19 billion. WhatsApp already offers a web interface for sending and receiving messages away from your phone, but it looks like something a bit more complex may be in the works.

Twitter account WABetaInfo, which keeps an eye on upcoming features from the various WhatsApp, err, apps, posted a series of screenshots earlier this week. They seem to indicate a collection of download buttons for Mac and Windows editions of WhatsApp, presumably taken from beta or internal versions of the WhatsApp website . (Update: a commenter pointed out that the screenshots appear to be from the WhatsApp translation page.) The formatting is rudimentary and broken in places, but the language is more or less in line with a standard software download page.

All of this is decidedly unconfirmed, but expanding into first-party apps for the two most popular desktop operating systems on the planet is well in line with WhatsApp's operating policy. After all, the company already offers apps for Windows Phone, BlackBerry OS, Nokia and Symbian devices - an unconventional but wildly successful "everything everywhere" strategy. If Windows and OS X clients appear, they should work the same way that the mobile and web versions do, allowing for logins and synching across devices with a single number. We'll be keeping an eye out for native clients in the next few months.