"Students and teachers can login to the DocHub app (or DocHub.com) using their Google account. From there, it is possible to upload any PDF, text document, or Microsoft Office file from Drive, the web, or even your computer/Chromebook download folder. Once a document had been uploaded, students can highlight, draw, insert text boxes, and even incorporate sticky notes. These annotated PDFs can then be sent to Drive or even shared with a link. Unlike some other web-based annotation tools, all of the annotations remain with the PDF after it has been sent to Drive though the sticky notes only appear when shared with a link."
NoteBookCast is a free whiteboard tool that will work in the web browser on a laptop, iPad, Android tablet, and Windows tablet. NoteBookCast is a collaborative whiteboard tool. You can invite others to join your whiteboard by entering the code assigned to your whiteboard. You can chat while drawing on NoteBookCast whiteboards.
Apps for presentation, screencasting, video making, file storage, whiteboard, PDF annotation, audio recording, notetaking, blogging, book creating, comic strips, digital storytelling, grading, midmapping, portfolios, posters, timelines, word clouds, speech to text
If you have been searching for an online collaboration tool that is versatile and easy to use, then Twiddla may be what you are looking for. Twiddla is a real-time collaboration whiteboard that allows an unlimited number of people to come together at one time to share or edit documents, images or websites.