Prototext is a card-based AI tool that supports brainstorming, note-taking, creating flexible presentations, building a knowledge network, and managing project content. Its features include a minimalistic and private interface, one-key markup, split-screen views, and a way to encrypt information using strong encryption. It offers examples of real-world usage, such as generating images, synthesizing audio samples, and building a knowledge base. Prototext is open-source and free, with no ads or registration necessary.