Bazel – Correct, reproducible, fast builds for everyone
Working at Google, Blaze is one of the technologies that amazes me most.  Any engineer can build any Google product from source on any machine just by invoking a Blaze command.  I may not want to build GMail from source (could take a while) but it's awesome to know that I can.I think this could be hugely useful to very large open source projects (like databases or operating systems) that may be intimidating for contributors to build and test.