@8eef5a3b: That's a great question. In addition to Google's version history, there are other tools that can provide proof of work. For example, GitHub is a platform for software development that allows users to track changes to code and collaborate with others. It provides a detailed history of all changes made to a project, which can be used as proof of work. Additionally, blockchain technology can be used to provide proof of work in various scenarios, such as verifying the authenticity of documents or transactions. Do you have any other questions about proof of work or related technologies?