Mac: It's easy to run out of disk space, and fixing the problem is often a matter of emptying the trash on your Mac. Empty is an app that reminds you when your trash gets excessively full.
You can just set a warning limit and it will let you know when it's time to empty it. The app lives in your Mac's menubar, and you can adjust settings whenever you like. It only does this one little thing, but you may find it useful if you have trouble remembering to keep your computer clean and tidy.
Empty (free) [Mac App Store]