This site is excellent as a teaching tool for students who are not familiar with Linux. I spent about 1 hour browsing through the various sections of each module and I was very impressed. The modules are very elementary, but for beginning Linux students, this would be an excellent way to learn the commands. It is easy to use and the students are given the opportunity to practice the commands, with immediate feedback on their success. There are also intermediate quizzes as well as an end of module quiz to test their skills.
The site uses pop-up windows for feedback and uses a good combination of text in the left window with an actual Linux command line in the right window.