Here are a couple pictures from the link. There are also labs online...not just a here's an experiment to do...but full on labs with critical thinking questions. There are animations, video clips, journaling ideas, and of course the digital textbook itself. There are units for energy, force and motion, weather, geology, and ecology. The "textbook" is downloadable into a pdf file and includes cross curricular links for other typical topics that middle school students study.
This is a picture from one of my favorite activities. It asks students to describe the energy transformations that are happening in this picture. Then students are asked to design and create one (Rube Goldberg machines) of their own. So POWERFUL!