I don't understand why people on HN are still recommending Telegram. It's not open, the crypto is highly questionable, and messages are not encrypted end-to-end by default (and not at all in groups). Use one of the apps that gets a full score in the EFF's Secure Messaging Scorecard [1], like Signal.
If you've got a better suggestion for secure group chats on iPhone, Android, Windows Phone, OS X, and Windows, please let me know! My family uses telegram extensively, but I'd love to replace it with something better if there's anything with similarly good UX on all of the platforms we use.
I'm not. I'm just saying that the majority of my friends are using it. For me it's better than skype and whatsapp. The GNU/Linux client works fine (although I'm not a big fan of its codebase: I had a look at it and guess what…)
It's true that not all of my criteria are included in the scorecard. For one thing, it's based on the statements of the developers, so if they say "it's encrypted", the EFF takes them at their word, and doesn't investigate the quality of the crypto. It also doesn't consider usability issues (secure defaults).
All my friends are on Whatsapp, and this is not nice... I'm going to try to convert them to Telegram., not easy.