Guide into free and open social networks for links

What are the main free and open social networks for links. NOTE: this howto is about the services/communities, not the software itself...

Description
We just want to know what are the online communities around social networks for links. They must be free and open. Complementary list here.

All the software used must be strictly Free Software and Open Source software. The service must be open to all free of charge. There must be plans to implement export your links to a file if you want or there must be an import/export feature or the possibility to export the hole database.

Solutions

 * qoosa
 * frassle
 * unalog still alpha (based on unalog)
 * de.lirio.us using rubic

Related guides

 * Guide to not so free and open social networks for links
 * Guide to podcasting communities and services
 * Guide to social networked shopping
 * Guide to social networks free software
 * Guide to social networks for blog links
 * Guide to free social networks where you can meet and interact with people

Related howtos

 * Howto share/synchronize bookmark between web browsers

External

 * socialsoftware blog