MailVu is a great tool for creating asynchronous interaction in either an online course or as part of a blended learning unit of work.
It enables asynchronous interaction with just a web-browser and a webcam or there is a free mobile app that runs on most platforms.
In this document you can find:
-: a step by step guide showing how to use it
-: a video tutorial that you can show to students
-: lots of suggestions and ideas for using it in the classroom or as part of an online course.