Signal
It allows Signal users with iOS, Android and a desktop app to send text messages, files, voice memos, images, GIF and video messages.
WeChat
Offered as an Android and iOS application, WeChat can also be used on Windows, Mac and web browser.
Telegram
Telegram, which has an application for phones, also has a web version like WhatsApp.
iMessage
You can use Apple's messaging application iMessage on Mac and iPhone.
Line
Line works on iOS, Android and Windows phones and also offers a desktop application for Windows and Mac.
Viber
Unlike WhatsApp and Telegram, you have to download a desktop client to use Viber on desktop.
BIP
The instant messaging application allows BIP users to chat as a group as well. The application also allows its users to video chat in HD quality.via: ntv.com.tr