Jami (formerly “Ring”) is a libre easy-to-use alternative to Skype, with voice call, video call and messaging.
It is open source and designed to respect its users’ privacy, with calls going directly from one user to another without using servers. It gives all its members a unique code, which they can share with others, so that they can add each other on the service.
Jitsi Meet is a free open source video chat app made by volunteers. You can use it through their website or through the mobile apps.
It is extremely easy to use: you don’t need to register, all you need to do is make up the name of a chat room and send the link to whoever you want to join you. You can also add a room password if you want.
BigBlueButton is a professional video conferencing tool focussed on online teaching and presenting. As such, it provides special features like slide-sharing, private and group chat, emoji feedback, polls, breakout rooms and many more.