WhatsApp is a messaging app that works on both Android and iOS devices. You can use WhatsApp to send text messages, images, videos, and even audio messages. It also supports messaging between users on different platforms, such as Android and iOS. There are other apps that work with WhatsApp, such as Telegram, Facebook Messenger, Viber, Line, and WeChat. All these services are compatible with WhatsApp and can be used to send and receive messages with people who have WhatsApp installed.