The secure and private Wire messenger app with end-to-end encryption is a great open source alternative for Whatsapp, Skype, Viber, WeChat, FB Messenger, Telegram. You don't need a cell phone number to login. These feature were attracting me and I can use it on almost all platforms (Linux. Android. iOS. Mac. Windows.) inclusive within the most common browsers.
There is also a standalone desktop version/client. How do I install the wire desktop client in Ubuntu?