Could be interesting. This is not only grammar. You find quiz, crossword puzzles and various other URLs like newspapers, carnevals and the Octoberfest in Munich. Notice that this site is still under construction but it is well organized. Many of the links are not active but try the first ones in each category and you'll have something to do.
Students often ask teachers about summer schools in Germany.
I think it might be of special interest to the students because here one can learn about everyday life in Germany. It has categories like 'taste', 'people', 'opinions' and 'celebrations'. The Oktoberfest in Munich has long been an FAQ of the students.