Well...i think most people would know about
Luminosity , one of my favourites ,
Only downside being , you have to pay , to use all of its features .
Lumosity offers a brain training program consisting of more than games and tests in the areas of memory, attention, flexibility, speed of processing, and problem solving. They offer daily challenges which are fun and a great way to start a day.
http://www.lumosity.com
and here's the good news ... for those who do not want to pay , here's a clone that's almost just as good and even more reputable
Welcome - Cambridge Brain Sciences