In truth there are many free link building directories. What you have found here is just one.

However it is important to note that this shouldn't be your only source of links. While you can quickly and easily build links from directories the engines will soon catch on if these are your only types of links and may begin penalizing the links.

Your best bet is a mix of directory links, combined with more traditional link building.

One thing I like to do for "traditional" link builiding is to look at my competitors links and see if I can get links from the same sources. This process can take a long time, but having these types of links can look more natural than directory only links.