Confluence

Confluence is a team workspace where you can create, collaborate, and organize all your work in one place. Dynamic pages give your team a place to create, capture, and collaborate on any project or idea. Spaces help your team structure, organize, and share work, so every team member has visibility into organisational knowledge and access to the information they need to do their best work. Confluence can be customized, by adding different categories and apps (e.g. Google Drive), to fit any department or project.

You can find out more in this demonstration video. It is free for up to 10 users, and for more users there is a pay version available.