You can use Brain Trainer by Luminosity, it's very good and addicting at the same time. It helps alot, I recommend you try it, and it's free, u can search it and just put "Luminosity" and it should pop up
You can use the Brain Shaper application which claims to improve concentration, put your brain into a meditative state, improve sleep, and invigorate the mind. The application combines binaural beats and a series of flashing light patterns that move your mind into various states of consciousness. You can find more from this link http://mac360.com/index.php/mac360/list/C7/.