Social bookmarking site such as Digg or Reddit is popular among advertisers and marketers. You can create an account for free and submit a favorite website. You'll get good backlinks and and SERP rather than traffic. (Some famous social bookmarking sites bring a lot of traffic!)

There are several open source social bookmarking scripts. You can develop your own brand social bookmarking site for free. Choose the powerful server you can afford, bookmarking script consumes CPU and memory usage. Check the spam posts frequently or implement Akismet service to prevent spam.



Drigg
http://www.drigg-code.org/
Drigg is a powerful Drupal module written by Tony Mobily, that allows you to promote stories automatically based on your users' votes. Unlike other Drupal and non-drupal solutions, you can do this with amazing simplicity.


GrabTheMic
http://sourceforge.net/projects/grabthemic/
GrabTheMic is an Open Source implementation of community-driven news sites such as Digg and Reddit. It is powered by Ruby on Rails.


Hotaru CMS
http://hotarucms.org/
Hotaru CMS is an open source, plugin-powered content management system. Like Digg, users can submit urls to news they wish to share with other users. These posts can be assigned to categories, given tags and edited. Other users can comment on and vote for the best posts, which are prominently displayed on the front page of the site.


PHPDug
http://www.kubelabs.com/phpdug/
Create a site where users can rate and comment on stories or sites posted by your users just like digg.com.


sabros.us
http://sourceforge.net/projects/sabrosus/
sabros.us is a CMS to put your bookmarks online with folksonomy support; just like del.icio.us, but the big diference is you will have the complete control of the source code and written on PHP with MySQL as backend we make it cross platform.


Scuttle
http://sourceforge.net/projects/scuttle/
Web-based social bookmarking system. Allows multiple users to store, share and tag their favourite links online.


SemanticScuttle
http://sourceforge.net/projects/semanticscuttle/
SemanticScuttle is a social bookmarking tool experimenting new features as structured tags or collaborative descriptions of tags.


Tagging manager
http://sourceforge.net/projects/taggingmanager/
Tagging Manager is a tool where each user can tag website's with meta-data. Features: Template based System, RSS-output, Multiuser Language support, Archive of tagged pages, Automatic tag-suggetions based on page metadata, Taxonomy-system.