We present an Open Geometry Textbook project whose main objective is to develop a web-based platform for acquiring geometric knowledge to form a textbook via the collective intelligence of a massive number of web users. The platform will provide a formal representation language for users to contribute formalized geometric knowledge contents and will integrate software tools for automated knowledge processing and content management. Collected geometric knowledge will be presented as a dynamic textbook, which can be freely accessed, timely updated, and soundly revised by any interested web user and whose authoritatively ideal versions will be published in print. We will design and implement effective mechanisms and tools for open textbook author identification, soundness checking, revision assessment, and version maintenance.