The first web 2.0 tool that I've found to be quite useful is Fit Brains. Fit Brains is a tool that mostly functions as brain training system.  Throughout a serios of games, students are able to train different skills of the brain such as memory, concentration, problem-solving and many more. 

Throughout education, no matter what you learn whether it be science, math, english language arts or any other course material for that matter, the use of your brain is common throughout all of it. These little games can allow the students to focus and train different assets of their brain in order to more efficiently succeed in their subjects. The games begin simple and easy such as matching or common patterns and will later increase in difficulty based on how far you continue to play. Also, after each activity a certain score will be given to you and the experience of a certain skill you're training is recorded. 

The greatest asset of this tool is the fact that it's simple yet efficient. Because your progress is recorded, the more you play the games, the more you own your skills. The pace at which you play the games is of no difference. Whether a slow learner plays or a fast learner plays, the only difference is the amount experience you earn. In the end, you still gradually train your brain which can help your education, 

The terms of service does not specify a certain age.