Ranked in these QuestionsQuestion Ranking
Pro Very lightweight file size
At 1.1MB, it's a lightweight program that you can set up quickly.
Available for Windows, Mac OSX, Android, iOS, and Linux.
Pro Free version has no time restrictions
The free version of the program has no time restrictions or nag screens, and you don't need to give your email when signing up.
Con No whiteboard
There are no whiteboard tools for drawing on the screen in order to clarify points.