This is my favorite flipped learning method because I've been a flash card learner all my life. When I first started teaching, I recommended that my students make flash cards of the words we learned. I even made PDF print outs of the those cards and distributed them after class. Not flipped! What good was it for my students to study the vocabulary after the lesson, when my goal was for them to use the vocabulary during the lesson?
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…