xHarbour is a portable implementation of the xBase language (Compiler & complete Run-time libraries). It's practically 100% backward compatible with CA-Clipper 5.2e and 5.3c, and offers many modern language extensions, and extensive Run-time libraries.
The Harbour Project is a Free Open Source Software effort to build a multiplatform Clipper language compiler. Harbour consists of the xBase language compiler and the runtime libraries with different terminal plugins and different databases (not just DBF)