Quill provides 150 writing and grammar activities built from 42 Common Core language standards. Students learn these concepts by proofreading passages and writing sentences, and they receive instant feedback on their work. Watch this video to find out more.
As the video suggests, Quill is primarily aimed at native speaker schoolchildren, but it could also be used in an ESL/EFL context with older learners (see here for an example), and would be particularly useful for those preparing exams such as IELTS or TOEFL, which contain a writing component. You'll find a lot more information on the Teacher Resources section of the Quill website. Quill is free to use, so why not check it out?