Perusall 
A web annotation tool.

Enables teachers to “Order and assign textbooks, articles, or your PDFs in Perusall. Students annotate the readings and asynchronously respond to each other’s comments and questions about the readings in context. With novel data analytics, Perusall automatically generates optimal student groupings and social interactions, grades students’ engagement to ensure they are prepared for class, and nudges those who need help to keep everyone on track.”

Perusall Support