Etherpad "is a highly customizable Open Source online editor providing collaborative editing in really real-time." It can be self-hosted (including through Cloudron) or used through one of the many third-party public instances available.
In a classroom, display an Etherpad pubicly with a projector and invite students to take notes on it together during lecture.
Generate questions together
During a guest speaker or webinar, have students compile questions for the speaker together on an Etherpad.
How to use it
- Google Docs