"LLDB is a modern debugger infrastructure which is built (like the rest of LLVM) as a series of modular and reusable libraries. LLDB builds on existing LLVM technologies like the enhanced disassembler APIs, the Clang ASTs and expression parser, the LLVM code generator and JIT compiler," according to the LLVM announcement by Chris Lattner.
The debugger is in its early stages of development. It only works on Mac with C, C++ and Objective C.
However, Lattner said, "LLDB is already much faster than GDB when debugging large programs, and has the promise to provide a much better user experience (particularly for C++ programmers)."
LLVM project started out as a research project at the University of Illinois. It's now an umbrella project for eight sub-projects, including LLDB.