Keybase is a great way to do company onboarding. Have a new employee setup a Keybase account (if they don't have one already) and now you have a simple and secure way to have conversations and exchange files (e.g. W-4 forms, insurance, etc)

I use it for personal communications too, so it is nice to use the same secure messaging platform for both work and personal and switch back and forth from computer to phone easily. I do wish the server portion and apps were opensource though.