WhatsApp - Synchronous communication

 

WhatsApp is a popular messaging app with end-to-end encrypted instant messaging that can be used on various platforms, including Android, iPhone and Windows smartphones, and Mac or Windows PCs.

The main draw of WhatsApp is it allows you to send and receive calls and messages using only an internet connection, which means it is virtually free to use and ideal for international calling. There are no fees to sign up, and no data plan allowances to worry about.