One of my favorite apps when I was in the classroom was called Explain Everything. Available for Android, iOS and Windows, this app allows teachers to quickly create a video recorded whiteboard lesson to share online.
There is a free version as well as a paid version, and I wholeheartedly recommend the $2.99 paid version. There's animation, loads of editing tools, and a 1-2 click option to upload to YouTube, or to simply save on your device. For schools that block the YouTube app, try uploading to SchoolTube (registration first).
I used Explain Everything mainly for math, but it can be used in other subject areas. It's quicker to do a video tutorial of "how to solve for a variable" than it is to demonstrate it in class. Between disruptive behavior, interruptions from outside sources, I was lucky to get a full 15 minutes of "how to" time. I would hook up my iPad to the data projector, and play the Explain Everything video to the class, with the announcement that this same video would be online for later reviewing. The video was about 3 minutes vs the 15 minutes I never seemed to have.
To view a lesson review created with Explain Everything, take a look at this YouTube video:
