In case you have missed the announcement, Tenable security has made the decision of commercializing the popular Nessus security scanner within the next month. 

As a result, a project group has been formed to release a GPL fork of the Nessus security scanner in the future.  This product will probably undergo a name change to prevent problems with support between the commercial scanner and the new GPL fork.  In the meantime, it is located at http://www.gnessus.org/doku.php .

Additionally, Handler Kevin Liston noted that another GPL nessus project is located at http://porz-wahn.berlios.de/homepage/about.php . 

Two more GPL projects to mention:

Segusius  (located at http://sourceforge.net/projects/segusius )
GPL Nesus Checks  (located at http://sourceforge.net/projects/gplnessuschecks )

(Thanks Schneelocke for reporting these)

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Scott Fendley
Handler on Duty