You can pre-record lessons for students using the apps below. Of course, students can also do the same to demonstrate their learning, even using WeVideo for collaborative work!
The options below enable you to record your screen, your face or both. Audio-only exports are also possible, so you can send (smaller) audio files for those who have limited bandwidth.
This is my favourite tool at the moment. You can make screencasts just like other apps - the advantage of this tool is you can also export animated gifs. This is perfect for embedding quick 'how tos' on slides, especially if students are being asked to use a new app. I can demo simple processes right in the slide and students don't have to wait for video-streaming.
If you use Loom to simultaneously record your screen and webcam, you appear in a circle (rather than a rectangle) at the bottom of the screen. This app is more streamlined than Screencastify, but there's not much difference between them. People seem to prefer one over the other depending on what they are more familiar with.
If you would like your students to create collaborative videos, WeVideo is like Google Docs but for video. Students can work together from wherever they are to create a product that they've all contributed to. At the moment, there are free upgrades that you can request here.