Telegram is a mobile/desktop messaging app with a focus on speed and security.
It seamlessly syncs across all of your devices and can be used on desktops, tablets and phones alike. You can send an unlimited amount of messages, photos, videos and files of any type (.doc, .zip, .pdf, etc.). Telegram groups have up to 5000 people, and you can send broadcasts to extensive contacts at the same time.
Telegram utilizes a network of worldwide servers to ensure that messages are processed fast by allowing you to connect to the closest one regardless of where you are and makes sure that those messages are heavily encrypted with time-tested algorithms.