Telegram

Cloud-based, cross-platform instant messaging (IM) focused on speed, security, and massive group capacity.

Telegram is a cloud-based, cross-platform IM service, prioritized for speed and robust security. It supports massive group chats (up to 200,000 members) and allows file sharing up to 2 GB per item, making it a powerful tool for large communities and businesses. The platform offers end-to-end encryption for voice/video calls and optional 'Secret Chats'; all other chats use a combination of 256-bit symmetric AES, 2048-bit RSA, and Diffie–Hellman encryption. Launched in 2013, Telegram has scaled significantly, surpassing 1 billion monthly active users as of March 2025.

https://telegram.org