Intel Thread Building Blocks (TBB) is a open source C++ library. Its aim complies with the one of OpenMP: taking advantage of multi-core processors without being an expert on parallel programming.
TBB provides a rich and pretended complete set of algorithms, containers, models and primitives for concurrent software. I would really call it the C++ library for concurrent programming. Though its great flexibility comes hand in hand with its complexity. You have to dig into the documentation for quite a while before you get you work done. And compared to OpenMP or Cilk++ you must understand more about concurrency.
Furthermore compared to OpenMP or Cilk++ your concurrent-enabled code looks very different to its sequential equivalent. TBB programs must be designed to use TBB from the beginning.