Textbooks often come as printed, linear, standalone, monolithic resources. However, teachers, more often than not, tend to draw from various sources to prepare their courses and modify or complement existing content. We describe a web platform for textbooks based on features of source-control management systems to enable teachers to tailor a specific textbook to their needs. Teachers can each create their own “fork” by reordering, adding, removing, or editing chapters and get clues on potentially broken backward or forward references.