Here is a biofeedback kit that uses red/infrared light sensing to measures changes in blood-oxygen level in your brain in real-time. HEGduino shows you in real time how your brain blood-oxygen levels respond to your thoughts and actions. As you focus, breath, and relax, you can watch the response on your screen.
The HEG can be controlled via WiFi, Bluetooth, and USB. It has a HTML interface and free game that you can play on your HTML5 compatible device. The developers are working on iOS/Android devices. The platform is open source.