Dropbox Paper is a place where you and your team can generate ideas together over an internet connection. Share any type of content, make changes to what you already have and get notified when someone else makes suggestions. The creativity flow has always better when teamwork.
GitHub Team Discussions is a way to help your team plan together, update one another and talk about any topic you'd like in discussion posts on your team's page in an organisation. Processes like planning, analysis, design, user research and general project decision making can now be done in one place.
Reactivepad is an online collaborative document editor that lets you put calculations directly inside your textual narrative - think of MS Word and MS Excel combined. It allows to create truly smart and reactive data-driven documents that are almost like apps!