Google forms can be easily made into quizzes that you can email your students and get their results. You can make multiple choice questions, questions requiring written answers. You can use them to test your student's knowledge (I send all my new students an A1-B2 Level Assessment quiz, so I can see in one glance what we need to work on and then automate my syllabus for each class and private student).

There are many ways to use audio in (and out of) your lessons. 

After private conversation lessons, I record my notes and send the 3-5 minute audio to the student along with a quick written transcript to the student. The whole process takes about 15 minutes, but my clients pay more for the service.

You can also send a listening lesson in advance, giving slower students…

Think of how often your class grinds to a halt because a few students are just not getting what you're laying down. In a typical 60 minute lesson, you have only a few minutes to elicit the target language, and if only a few students are still confused, you have to make a decision—move along with your lesson or pause and try to re-explain (if you can). When that happens, it's hard to…