If you've got a website or a blog, chances are you can use some of these free web tools. You can check the PageRank of your site or sites, check the Alexa rank, check backlinks, and see how fast your site loads - and that's just the beginning. There are also tools to encrypt and optimize your html, shorten links, and clean and remove duplicates from lists.
It's nice having these tools all in one place. If there's one you plan to use on a regular basis or want to let your visitors use, they also provide the code so you can add the tool to your own site.