Check out quill.org. We're an open source tool for learning English grammar. We've got an active community of developers at https://github.com/empirical-org/qui

Check out quill.org. We're an open source tool for learning English grammar. We've got an active community of developers at https://github.com/empirical-org/quill https://github.com/empirical-org/quill, and we currently have about 500 students using our site per day. There are a variety of front end and back end projects. Feel free to reach me at peter (at) quill (dot) org.