Although I usually provide tools or tricks more focused on student use and success, this one is great for teachers.
Formative is a tool that provides teachers with tools to engage, instruct, and assess their students.
Just a few of the things you can do with Formative include transforming a PDF or Google Doc into an auto-graded quiz, enhancing reading passages with questions, promoting higher-level thinking with advanced Math tools, and unleashing student creativity with the option of audio and video responses.
Check out Formative for yourself.