WhatsApp is now available as a Windows or OS X app.

WhatsApp, the massively popular smartphone messaging app owned by Facebook Inc., is now available in a familiar place: your computer’s desktop. On Tuesday, WhatsApp released apps for Apple Inc.’s OS X for Mac computers, and Microsoft Corp.’s Windows 8 and Windows 10 for PCs.

The app experience mimics what you get on the phone: You can send text, photos, video and audio files to friends and family. The reason people will download the app is that it brings over a key smartphone feature: live notifications, crucial for real-time chat.

By landing on Macs and PCs, WhatsApp is now present on every major OS, including Apple’s iOS, Alphabet Inc.’s Android, BlackBerry and Windows phone—and even in Web browsers. A fully cross-platform messaging service with more than 1 billion users world-wide could pose a threat to competitors, especially Apple’s iMessage and Microsoft’s Skype.

Apple’s iMessage lets you receive messages on a Mac and iOS mobile device, but it is absent on Windows PCs and Android phones. Google’s alternative, Hangouts, is more ubiquitous, but while it enjoyed some success with corporate clients, it never really took off as a populist option. Facebook Messenger, WhatsApp’s sibling rival, is available on mobile, in the Web and as a Windows 8 or 10 app, but it doesn’t have an official OS X app so far. (In case you’re wondering, the wildly popular Snapchat is only available on iOS and Android.)

Skype, with 300 million users at last count, is the only other messaging service that lets you start conversations on your smartphone (iOS, Android, Windows phone or BlackBerry) and continue them on any computer desktop (via the Web, or using an OS X or Windows app). It is popular for its video and audio calling features, and isn’t as common a platform for texting. WhatsApp has bulked up in multimedia options over the past few years, but still lacks Skype’s ability to make real-time video calls.