The dlvhex Solver is a C++ software for computing answer sets of logic programs with external sources. During my PhD, I performed a rewrite of the software to make it more efficient. After my PhD, Christoph Redl continued to improve the software in his PhD.
The core of dlvhex is available at github.com/hexhex/core.
Several plugins are available at github.com/hexhex/.
For details please see The homepage of dlvhex.