What are some alternatives?
When comparing Contus Fly and Telegram, you can also consider the following products
Slack - A messaging app for teams who see through the Earth!
Discord - Step up your game with a modern voice & text chat app. Crystal clear voice, multiple server and channel support, mobile apps, and more.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Zulip - Powerful open source group chat
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Twilio - Brings voice and messaging to your web and mobile applications.