If you use Gmail, Google Classroom, Google Slides, and/or Google Documents, you can now add recorded audio notes and feedback directly to each product, using the Mote app, available at https://www.justmote.me/. Students do not need to have Mote installed to listen to your notes, but if they do have it, they can respond.
Mote offers a free plan that allows you to record for up to 30 seconds. You can make as many 30-second recordings as you like. There are also paid plans (either $19 or $39 per year) that allow longer recordings and recording transcription
Mote’s homepage, https://www.justmote.me/, includes a video that explains how to add the Mote extension.
Here also is a video that shows how Mote looks to students: https://www.youtube.com/watch?v=Mf-3bc7QrJA