For those using WhatsApp, LINE, and BlackBerry® Messenger™, have a closer look to Telegram. For those looking for alternative, look at Telegram. For those concerning Free Software a lot, have a same look. We will find that Telegram is a real communication system. In Free Software matter, Telegram is better than 3 mentioned above.
1. GNU GPL Licenses
Have a closer look at https://telegram.org/apps. GPL v2 and v3 stated there for various version of Telegram clients. Telegram is Free Software.
2. Source Code
Have a closer look at https://github.com/telegramdesktop/tdesktop at least. We can see the source code. Grab it. Study it. Modify it. Of course under Free Software license GNU GPL. So any competent person can measure how secure Telegram is.
3. Desktop Clients for GNU/Linux
Have a closer look at https://desktop.telegram.org. It is the official client directly from Telegram developer. We can install Telegram client in GNU/Linux desktop. Does WhatsApp, LINE, or BlackBerry® Messenger™ give it? No. They abandon GNU/Linux desktop.
Have a closer look at https://telegram.org/faq#q-how-secure-is-telegram section. Have a look at the new secure protocol named MTProto https://core.telegram.org/mtproto. Have a look at its security hacking contest https://telegram.org/faq#q-what-if-my-hacker-friend-says-they-could-decipher-telegram-mes.
Have a closer look at https://telegram.org/privacy. Telegram cares about our privacy. No ads in Telegram. No user data collection. Easy removal for our previously saved data.
Have a closer look at https://core.telegram.org/api. Telegram API is open to everyone. So we knew CuteGram desktop client exists. So do Telegram-FOSS, Jollagram, and Sailorgram exist. They can use the API freely. They extend Telegram in much broader way in many platforms.
Have a closer look at https://telegram.org/faq#q-how-are-you-going-to-make-money-out-of-this. Telegram doesn’t open a donation yet. They are supported by a company named Digital Fortress to run it all.
Telegram is a really free cloud-based communication system to replace WhatsApp, LINE, or BlackBerry® Messenger™. Anyone concerns about Free Software can use it.