Knotable - Cut the noise out of busy email threads
Sketchboard.io - Visual Remote Teamwork. Solve problems and create ideas on endless whiteboard with your teammates by sketching.
Scrapbox - A new style of note-taking that lets you create, discuss, and learn together in one self-organizing space.
Limnu - Sketch, share and collaborate with your team
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
Draw.Chat - Anonymous real-time whiteboard with text and video chat.