Adaptive Learning Games
Sometimes the simplest solution is the best. These games are not exceptionally high tech but they are effective.
I tried out the comma game and the one about chemical families. It was somewhat like flashcards but the game gave me instant feedback. This one feature was enough to make this site blogworthy.
Use the search feature in the upper right corner to find more games.
I searched for water to see what options I had to pick from. So many to choose from!