Box Notes is a very well designed and intuitive tool you can use to capture and expand your ideas. Collaborate with others on the same document at the same time, see who’s annotating/changing what and share your ideas with others.
Box Notes is meant to be used along the Box cloud storage solutions so you’ll have to create a (free) account to start with. Since Box Notes is built on top of Box, sharing notes with others is just as simple and secure as sharing anything else on Box. If you create a note in a folder that’s already shared with others, you don’t have to do anything else but to save your note, and your teammates will have instant access.