Cost: free and premium
Flipgrid is a video discussion platform.
https://docs.google.com/document
Cost: Free.
Google Docs is used to create documents, Google Sheets for spreadsheets, and Google Slides for slidesets – these can be created individually or collaboratively.
Cost: Free and premium versions
Padlet is a collaborative multi media bulletin board where learners can share links, documents, videos, and discussions.
Cost: Free
Perusall is an interactive document tool that allows you to annotate pdfs, and websites collaboratively.
https://uwaterloo.ca/keep-learning/tools-and-technology/perusall
Cost: Free and premium versions
Slack is a robust messaging app intended for teams. Discussions are organized via "channels", which can be public or private. Slack allows for sharing of documents and links. Slack also integrates with a variety of apps.