''Originally known as XDB, this C++ library (both URLs refer to the same project) is for manipulating DBaseIII (.DBF) files.''
*** http://linux.techass.com/projects/xdb/
*** http://sourceforge.net/projects/xdb/ 

It has been renamed to Xbase -- possibly to avoid confusion with another XDB.  There appear to have been a number of efforts under the XDB name, mostly involving XML or object databases.  There may have been a distributed database effort known as XDB (see discussion on SemanticWebIsStupid), but I can't find any reference to it, unless Oracle's XML DB (http://www.oracle.com/technology/tech/xml/xmldb/index.html) -- known as XDB at one point, I think -- is what it has evolved into. 

----
Related:
* ExBase
* Xbase and SQL
* DebianLinux Package of xbsql