Nathan Hall's long list of registration-free web tools for students. Nathan's list is divided into twenty-five categories. Some of the categories of most interest to teachers are online whiteboards, survey/ poll tools, chart/ graph tools, annotation tools, document creation tools, and photo & drawing tools.
Applications for Education
Using web tools that don't require registration to use can save you and your students time as you can jump right into an activity without having to struggle with usernames and passwords. The downside to using registration-free web tools is that often you don't have an option for saving your work other than downloading it directly to your computer or sharing it to another service like Evernote or Google Drive which do require registration.