Circus Ponies' Notebook is one of the most mature productivity apps on the Mac. Its developer, Jayson Adams, is a stand-up guy that has been pouring himself into this application for a long time. Over the past several years, Jayson and his team have been hard at work in a big update that just went live. I haven't tried the new version yet but a lot of people like it. Courtney Stafford Hickey gives it thumbs up over at iPhone JD. Notebook's appeal is the idea of one app to hold all your data. I know students that use it exclusively and lawyers that run entire lawsuits through Notebook. If you've not seen it before, it is definitely worth checking out.