Spitfire can be used as a simple task board, in agile retrospectives or brainstorming sessions, simply whenever teams are working across different locations and want to have immediate feedback on content change.
Go to spitfire.peewee.space, create a whiteboard session, and share the URL with the people you want to work with. Anyone who has access to that URL can participate in your work.
Spitfire is free to use for everyone. I am building it on top of the Meteor platform while obeying the agile mantra: Make the simplest thing that will possibly work now. Validate. Repeat. Yay. Spitfire is Open Source. Find the code on GitHub.