Windows/Mac: WhatsApp is working hard to become your go-to messenger. Now that it's free for everyone, you can use WhatsApp on your computer with the new desktop apps. When you first login to WhatsApp on the desktop, you'll be prompted to scan a code from the mobile WhatsApp app on your phone. You can insert your own Yo Dawg joke here. To scan the code from your phone, press the menu button in WhatsApp and tap WhatsApp Web. Here you can scan the QR code on your computer. Later, you can also view a list of all desktop or web clients that are logged into your account from this menu.
The desktop app works much like WhatsApp Web. You can send messages, attachments and pictures; record voice messages; and manage your message history. It might be missing a couple of features from the phone version (I can't find a way to change a conversation wallpaper from the desktop version, for example) but it should be mostly the same experience you're used to.
Introducing WhatsApp's desktop app [WhatsApp]