Sounds like you need a process, rather than a tool. Personally, I jot down everything that gets mentioned to me on paper and, within 1-2 days, it will end up in the project management system (if it is something to be worked on). Once it's there, I strike it through in my notepad. So basically, 99% of my notepad is a scribble - only 1% that I need to think about remains un-struck.