NovelAI is an AI tool that assists with authorship, storytelling, and virtual companionship. It uses AI algorithms to generate human-like writing based on user input, enabling anyone to produce quality literature regardless of their ability. Users have unprecedented freedom in natural language processing playgrounds and can train the AI in real literature. The tool offers features like visual character image generation, power image models, and the ability to create custom AI modules and themes. It has various pricing tiers with different features and benefits.