Imo.im

imo is a free audio/video calling and instant messaging software service. It allows sending music, video, PDFs and other files, along with various free stickers. It supports encrypted group video and voice calls with up to 20 participants. According to its developer, the service possesses over 200 million users and over 50 million messages per day are sent through it.
History.
The product was created as a web-based application in 2005 for accessing multiple chat platforms, including Facebook Messenger, Google Talk, Yahoo! Messenger, and Skype chat. It was developed by PageBites, and required one's phone number to verify the users' account. In March 2014, support for all third-party messaging networks ended.
In Jan 2018, the app reached 500 million installs.