There's more than one billion monthly active WhatsApp users and now everyone will be able to access it from a computer as well as their phones, because a WhatsApp desktop app has just been launched.
Technically you could already access the service from a computer using WhatsApp Web, but where that lives in a web browser the desktop app runs natively on your machine, so you don't need an internet window open - plus there's support for native desktop notifications and better keyboard shortcuts.
You still need to be running WhatsApp on your phone to use it, the app simply mirrors the messages, but if you're sat at a computer it's a lot faster and easier to message people from there, using a full sized keyboard, than switch to a tiny touchscreen.
Challenging the competition
It also brings the messaging service more in line with the likes of Skype, which has full support for both desktop and mobile use, though the fact that WhatsApp still needs to be running on your phone too means it's not quite a match.