Goo.gl to create, distribute, and track use of shortened URLs. After posting that tutorial on Facebook someone asked if it was possible to make the shortened URL private. Unfortunately, Goo.gl doesn't let you do that, but there are services that will let you do that. Thinfi is one of those services that lets you create shortened, password-protected URLs. In the video embedded below I provide a short demonstration of how to use Thinfi.
Applications for Education
As I mentioned in the video, Thinfi could be a good tool to use when you want to share a preview of a project before it is ready for public consumption. For example, if my students are working on developing websites and they want to gather feedback before showing the site to the whole world, sharing a password-protected URL could be a good way to do that.