"Productivity Tool" is often an oxymoron. I know countless hours have been wasted trying to find the perfect  productivity tool or solution. That said, I have recently settled on a tool that seems to work for me - Things.

Things is a productivity tool for the mac written by Cultured Code. The application is beautifully written, simple and even works for those who follow GTD (getting things done). It has a very well thought out interface and uses tags for organisation and context setting.

For those of you who use an iPhone, Things is also available as a native iPhone application, which syncs nicely with the desktop app. Prior to using Things I was using OmniFocus, however I found it overly complex for my needs in comparison to Things. Certainly an application worth a look.