As teachers gain practical experience, they develop best practices, often exploring and refining personal innovations as part of their pedagogy. However, many of these good ideas are practiced in isolation - there is little infrastructure for sharing and knowledge management in schools. We describe Teacher Bridge, a suite of tools and an associated online community for teachers' professional development. Teachers can use these tools to build online activities for their students and for themselves. Because the teachers develop these activities as part of an online community, the resulting content can be explored and used by other educators, either in direct support of their own teaching goals, or as a model for related activities. We report on the design process we followed to create Teacher Bridge and discuss how we have used it to create an online community of teacher developers.