I have previously used Haiku Deck and like that it works on iPads and Chromebooks.
Educreations is one of my favorite free apps. I like that teachers can easily create a lesson to help their students and after entering some information about the video it is automatically uploaded and students can start accessing it right away. I am also a fan of their student to teacher capabilities. When a teacher sets up a class they are able to have student join and their videos will be sent to the teacher. Educreations also lets you record on a Chromebook and the videos can be viewed on many platforms.