Most of us are familiar with Skype. Skype is a great free tool for distance communication. It supports chat, voice and video calls, conference calls, sharing of screen and sending documents. You can join through the Skype Desktop tool, from the mobile phone app or through a browser. The performance in terms of connection can be a bit less than other tools however.
Google Hangouts is also often used. It offers similar features as Skype. It integrates well with the Google applications and GMail. A description of features can be found here.
Another option is the free version of Zoom. Zoom has an intuitive interface and good performance. With the free version of Zoom you have unlimited sessions with one person and max. 40 minutes with up to 100 participants. Zoom, however, has serious issues with security and privacy and is therefore not recommended as corporate solution.
Read more about privacy and security issues with Zoom
If you’re looking for a free and 100% Open Source solution Jitsi is a great tool. On your computer it runs from the browser. For the mobile phone there’s an app. It allows video conferencing, chat and screen sharing. It's much safer than Zoom. Read here about the safety of Jitsi. It's very democratic: you can mute all users, but they can only unmute themselves. It has raise hand functionality and you can start a YouTube video in a Jitsi session to watch simultaneously with all viewers. You can record Zoom sessions and they are saved directly into Dropbox.