Wikipedia is the best free tool to build backlinks to any website. Anyway, your links must be educative, informative and unique. Just submit your web pages to Wikipedia under related links, and it will give you a lot of organic visits every month for free.
Dmoz is another amazing website for link building. You can submit your links to http://dmoz-odp.org/ and get free web visitors frequently. As we mentioned on Wikipedia, your links must be legit. Dmoz is a great tool to increase web traffic rankings.
NOTE: Dmoz open directory project is shut down right now.
SoMuch is another open directory to submit your website to get dofollow links. Visit, https://somuch.com and submit your website to get listed. It will generate you extra visitors organically to your website.
viesearch.com has web directory listing feature and it has more than 500,000 linked domains. Submit your website to https://viesearch.com and generate unlimited free traffic to your website among their web directory.
GainWeb is also another web directory that you can use to boost web traffic rankings. Visit http://www.gainweb.org and submit your website to get listed free.