ChatFast is a platform that enables users to create custom GPT chatbots using their own data. The service includes features for training chatbots with various data types such as text files, PDFs, and website links. Users can correct and improve chatbot responses with custom Q&A, capture visitor information through natural language interaction, and create custom forms that are triggered by AI. The chatbots can be embedded in websites and are designed to interact with visitors, understand their intent, and provide personalized experiences.