ConceptGcc is a prototype compiler implementing ConceptCpp by extending GnuCpp.
http://www.generic-programming.org/software/ConceptGCC/
There is an example of its use on ConceptCpp.
In October 2008 the source code archive of ConceptGcc was moved (see http://www.osl.iu.edu/MailArchives/conceptgcc/2008/10/0173.php).
The source code to ConceptGCC has moved into the Free Software Foundation GCC repository, and all rights have been assigned over to the FSF. At present, the code lives on the aptly-named conceptgcc-branch, which I hope can be used to help stage in concepts support for a future version of GCC.
The ConceptGCC repository currently hosted by Indiana University will stay up, but it won't be receiving any additional changes. All new development should be done in the FSF GCC repository.
-- Doug Gregor
Support for various features of CeePlusPlusEleven, (no longer including concepts), are summarised at http://gcc.gnu.org/projects/cxx0x.html
2011 There is now a new implementation of concepts, ConceptClang, being made for CeePlusPlus in a version of Clang (CeeLanguageFamilyFrontEnd).