Padlet is an online tool for brainstorming.
In Padlet, you can set up a 'collaborative board'. You can choose from different structures, such as a grid, backchannel or stream. If you share a Padlet with students, they can add texts, images, videos, links and more. If you allow it, students can also rate, and reply to each other's posts.
Example of an assignment using Padlet:
Post your thesis statements for your essay to the Padlet (created by the teacher). Comment on each other's statements. Are they debateable?