Sometimes you need a tool for a specific lesson or activity that you aren’t likely to use that often. The time it takes for students to sign up and then remember the username/password for the few times you need it creates a barrier for using that tool. In these situations it is easier to use tools that do not require students to create an account.
Nathan Hall has created an exhaustive list of different technology tools that have can be used for lesson or activities that don’t require students to create an account. Some of my favorites on the list include: Padlet (digital corkboard tool), Bounce (image annotation tool), and Graph.tk (mathematical graph creator).
All of these tools make it easy for students to focus on the task in the lesson rather than creating and managing multiple accounts.
Source: Webtools: No Registration Needed for Students