Access
At one point in time I was writing a web PIM which followed all the GTD concepts, but life and requirements got in the way and the project fell off track. I have recently gotten back into GTD and I am working on a stand-alone app that uses a Microsoft Access database backend. The database is rather full-fledged, and lends itself better to having an application GUI sitting on top of it rather than casual use, but I would be happy to throw it your way if you like....or you can just wait for me to finish the app.