Traffic Light! Free - great tool to project onto screen, control when students start a project, project a yellow when the activity should be wrapping up, and red for stop. Grades 1-8, or HS just for a time of fun.
Teach: Interactive Whiteboard, similar to ShowMe or Educreations with more features...still think Explain Everything is the best. Knowmia also has a web based component that Explain Everything doesn't!