This paper introduces hyperobjects, a linguistic mechanism that allows different branches of a multithreaded program to maintain coordinated local views of the same nonlocal variable. We have identified three kinds of hyperobjects that seem to be useful -- reducers, holders, and splitters -- and we have implemented reducers and holders in Cilk++, a set of extensions to the C++ programming language that enables "dynamic" multithreaded programming in the style of MIT Cilk. We analyze a randomized locking methodology for reducers and show that a work-stealing scheduler can support reducers without incurring significant overhead.