Whether you're working from home or looking for a way to chat with others using video, Skype has broken traditional barriers to communication. Along with chatting with people in your in-app contacts, you can also use it to make international calls. If the person you're talking to also uses a Skype account, talking to them doesn't cost anything extra. For an extra charge, however, you can call and text your non-Skype contacts on their cellphones.
Skype debuted in 2003 in the early days of VoIP. Its ownership changed hands a couple of times before Microsoft acquired it in 2011.
Skype is no longer the most popular VoIP because communication has become mobile. Other apps such as WhatsApp and Viber have been more successful on mobile devices than Skype.