Bazel, Google build system
In a wonderful sense of - irony? - Google has made a cross-platform build system that supports Linux and OS X, but not (yet) Windows.
Building a Build System: Bazel reaches Beta
Bazel home page.
Bazel GitHub repo
According to the released info, Bazel is now used to build most software at Google. Someday we’ll see unification on build tools? We still have independent ecosystems.