NowComment has the most sophisticated collaboration tools available for group discussion, annotation, and curation of texts, images, and videos.
It displays threaded commenting alongside the sentences and paragraphs of texts, the areas of images, and timestamps of videos to create engaging online conversations literally in context. Brainstorm, debate, and collaborate as never before!
Twiddla is a free, no-setup, web-based meeting playground. Mark up websites, graphics, and photos, or start brainstorming on a blank canvas. Voice and Text chat too!
CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images. No registration or plugins required.