DiffTastic is a free and open-source tool for generating visual diffs of HTML documents. It can compare two versions of a document and highlight the differences between them. DiffTastic is designed to be easy to use, with a simple interface and clear instructions. It can be used to compare any type of HTML document, including web pages, emails, and code snippets. DiffTastic is a valuable tool for web developers, designers, and anyone else who needs to compare two versions of a document.