Some learning situations may require further customization not possible via pre-fabricated content. In these situations, the teacher must seek tools for enhancing text as opposed to already enhanced text. One of the gems of the web is the CAST UDL Book Builder, a free digital book database and book builder. Developed and hosted by the Center for Applied Special Technology (CAST), Book Builder helps educators “create, share, publish, and read digital books that support diverse learners according to their individual needs, interests, and skills.” The database and tool integrate a number of technologies like screen-reading software to make content accessible to students with learning disabilities, yet at the same time integrating functionality that engages the reader through the use of built-in avatars who pose questions and offer ideas as the students reads.