I've been working on a sideline project for a little while. Its called mentronome. It is about measuring your mental awareness and recording it over time. It includes an interface to the Neurosky Mindwave EEG device (see below).
I've decided to release the source code for the desktop client. I just wanted to record one amazingly obvious and practical reason why this is a good idea: If users (and people are signing up to use the site from all over the world!) have issues with the software, what is the easiest way to support them? Give them the source code so they can troubleshoot it themselves. Never mind the fact that the project is built on a number of great open source technologies: Python, Ruby, Rails to name but a few. The ability to empower users of your software (and possibly feed back improvements they make) is the most compelling argument for open source.
Do keep an eye on the mentronome site. I have some great improvements planned: usage statistics, user badges, mobile clients and support for more EEG headsets. By releasing the client source today, I hope to "give back" to the open source community in my own small way as well as improving the service mentronome provides.
So check it out! The source code is hosted on bitbucket.