I've been looking around today trying to decide on a topic for next week and see what was snazzy and new out there. One of the tools that I came across is called "Function Carnival", which would be the perfect addition to a graphing unit in a math class or to a physics class. The idea is pretty simple. The student watches a video clip and then draws a graph based on the motion. Once they click play, the clip is played again with a secondary moving object that matches the graph so they can see how accurate they were. You can set up a classroom for them to do the exercises, and they have a teacher tip section on this website. I played with it for a while and it certainly has potential to get your students involved and spur some conversation about what happens. It's pretty fun!
I had a teacher ask me if there was a way to hide or remove students who are no longer in your class. The answer is maybe. It depends on if they are officially dropped from your class and appearing as red in your roster and gradebook. If not, then no, you cannot remove them until they have been unenrolled from the class. If the student is showing up as red in your gradebook though, you can hide them so you don't have to worry about them. Here is a screenshot to help you do it: