Which instant messaging app best supports multiple IM clients?

WhatsApp is widely known to be the world's most popular messaging app. Here's more proof to it. According to recent research from digital market intelligence company SimilarWeb, WhatsApp is the top mobile messaging app in 109 countries across the world. In India, Facebook-owned Whatsapp is installed on 94.8% of all Android devices and is used for an average of 37 minutes daily, according to the report.Of the 187 countries that SimilarWeb surveyed, WhatsApp emerged as a clear leader on 109 nations, or 55.6% of the world. Other than India, other countries where the messaging app has a strong user base are include Brazil, Mexico, UK, Russia, and several countries in South AmericaFacebook's Messenger app came in second overall, claiming 49 countries including Australia, Canada, and the US.After Messenger, Viber was the only other messaging app which has a strong presence in 10 or more countries. The app shows strong popularity in Eastern Europe, and is the top app in Belarus, Moldova, Ukraine, and others.