Telegram - one of the most popular, to date, instant messengers. Such popularity is due to high speed, wide functionality, ease of use and a high degree of security.
Description of Telegram
Pure instant messaging — simple, fast, secure, and synced across all your devices. One of the world's top 10 most downloaded apps with over 500 million active users.
FAST: Telegram is the fastest messaging app on the market, connecting people via a unique, distributed network of data centers around the globe.
SYNCED: You can access your messages from all your phones, tablets and computers at once. Telegram apps are standalone, so you don’t need to keep your phone connected. Start typing on one device and finish the message from another. Never lose your data again.
UNLIMITED: You can send media and files, without any limits on their type and size. Your entire chat history will require no disk space on your device, and will be securely stored in the Telegram cloud for as long as you need it.
SECURE: We made it our mission to provide the best security combined with ease of use. Everything on Telegram, including chats, groups, media, etc. is encrypted using a combination of 256-bit symmetric AES encryption, 2048-bit RSA encryption, and Diffie–Hellman secure key exchange.
100% FREE & OPEN: Telegram has a fully documented and free API for developers, open source apps and verifiable builds to prove the app you download is built from the exact same source code that is published.