For anybody with a bit of imagination and a talented programmer, creating a tool for your site is the easiest way to link bait. Make the tool useful and well presented and its very easy to link to. Unique and useful tools can often turn a commercial site that struggles to attract any natural links into a useful resource that even competitors will link to and use on a regular basis.
Common ideas include methods to help people find information about products, test their websites, improve their skills, generate images or content for blogs and social networking profiles. Some of the best tools build millions of links without the users even knowing they are part of some clever link bait campaign.