It would seem that lots of people out there are getting things done, judging by the number of Getting Things Done applications that are coming out. Actiontastic, now in beta, is another entry into the GTD market on OS X. The power of Actiontastic, according to its developer, is in the simplicity of the app. I come from a long line of unorganized Irish people, so I am not an able judge of this app. I can tell you that it has the best name of any of the GTD apps I have come across.
This is a free beta, but it is a beta so downloader beware.