Ghost Note ($9.99, try before you buy) offers a really clever OS X utility. It evaluates the context of your current work state, whether you’re in a web browser, or selecting a file in the Finder, or editing a document in Photoshop, and it enables you to add comments to the context of your work.
For example, the screenshot at this top of this write-up shows a note that only appears when I’m working on new posts. That means I can keep a running log that’s specific to my task, and it’s always ready and available when I’m working in that context.
It’s rare to find a utility that’s both novel and so well thought out.
I had a few qualms in usage, primarily tied to the thinness of the fonts (mostly due to my weak eyes) but on the whole, I really liked the concept and the implementation. You can change the background of the note for better contrast. I went with yellow over black in the end.
Be aware that you need to install scripts to support some of the context inference. These are added to your Documents folder as Apple Scripts and are mostly harmless. However, context-sensing is incomplete and you may need to add and customize those scripts if your tasks extend beyond those already supported.
The app offers you a one-week trial period. I encourage you to kick its wheels. Nice find!