A video chat and video conferencing service hosted by Google.
Slack is a workplace communication tool, where participants can message each other, create channels/discussion groups, and share tools and files. Slack also integrates with other apps/add-ins and other workplace tools.
Discord is a community-building tool where you can connect over voice, video, and text chat. Discord uses text channels to chat over text, and voice channels where you can use voice and video.
Zoom Meeting is a video platform you can use to communicate with Newcomers through video meetings, text chat, audio/phone, webinars, interactive sessions, and online events.