The number one feature I wish WhatsApp (and Signal) would adopt. I don't care for either service, but that would at least allow me or my partner to occasionally participate in group chats without resorting to buying an Android or IOS smartphone.
People just assume everyone under 60 has WhatsApp in some countries (the Netherlands being one of them), and it borders on being a requirement to function socially.
My partner went to a course for pregnant women, and during the first meeting it was agreed that all communication outside of the meetings would go via WhatsApp, but the course leader would send emails to my partner for changes in scheduling. (My partner has no smartphone, and doesn't want one either, but she owns a modern laptop and works in IT.) So basically any knowledge and questions shared in the group are invisible to her.
This situation is likely to come up again and again as we start raising a child, and all we can do to remedy it is buy a smartphone with one of the pre-approved operating systems, and join the social graph of Facebook…
You can use Signal on Desktop without your phone being online. (This does not work with WhatsApp.)
Use Signal if you absolutely need end to end encryption, extremely secure chat, and no way to use it outside of your phone being on and connected to the Internet.
Use Telegram if you want chat. Don't except high levels of security and for the average user who already uses Facebook Messenger and Instagram, it's good enough.