Duro is a relational open-source database library written in C http://duro.sourceforge.net/ . It is based on the principles laid down in the book Foundation for Future Database Systems: The Third Manifesto by C. J. Date and Hugh Darwen.
The goal of the Duro project is to create a library which is as compliant with the proposed database language D as it is possible for a C library. This library is supposed to serve as a basis for a truly relational database management system (TRDBMS).
Duro is published under the terms of the GNU General Public License.
The current release of Duro is 0.12, released 2012-10-31. Some features:
escargo 1 Aug 2005 - This is just begging for confusion between the D programming Language[L1 ], viewed by its creators as a reengineering of C and C++, and this other proposed database language D[L2 ]. There are only so many letters of the alphabet, and there are probably programming languages for each of them. (I seem to remember a couple based on alternative pronunciations: Eh and Zed, both originating out of Canada, as I recall.)
Also see TclRAL.