Several Web sites offer RSS feeds, but they do not necessarily cover the type of information you are looking for, and there aren't many tools to check local files.
Changes Meter does this exact job for you and it will notify you with a colorful, useful, and unobtrusive pie-chart icon on the menu bar.
- Final release, it will be replaced by a new app currently under development
- Works fine on OS X 10.10 Yosemite
- OS X 10.7.5 or later
*Previously available here