If there's one tool that I have found to be beneficial during #covid19 social distancing, it's Keybase.
While it doesn't have the audio/video calling of others, it has provided the most consistent experience in a messaging platform, with privacy and security as a key focus.
If someone were wanting to move their certain social group to an online system, Keybase is a great option.
It has a better user experience on all devices than other privacy-minded systems, and has some great non-messaging features like file sharing to round things out.
Last year, I went through all the free secure messaging platforms I could find, and Keybase was one of the three "finalists": https://levisan.me/blog/encrypted-messenger-showdown
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!