My whole extended (Dutch and Swedish) family uses it, mostly due to a distaste of Facebook (so no Whatsapp or FB messenger). It has the advantage of seamlessly joining mobile and desktop versions (for normal conversations, this does not work for device-to-device 'secret' chats) and can be accessed through several free software implementations for the client (including a command line client for Linux). I'm still waiting for a self-hosted server but not holding my breath. Depending on the behaviour of Telegram, Inc. I'll eventually migrate to a self-hosted alternative or try my hand at a self-hosted server implementation.