What is "telegram"
Telegram is available for smartphones or tablets (Android, iOS, Windows Phone, Ubuntu Touch, Firefox OS), computers (Windows, OS X, Linux) and also as Web App.
Users can send messages and exchange photos, videos, stickers and files of any type.
Telegram also has optional end-to-end encryption. Telegram clients have open source, but their servers are proprietary.
The service also provides Apis for independent developers.