From Cloudius comes OSv: An alternative to Linux running in a virtual machine, written in modern C++. Cloudius is a startup formed by a group of ex-Red Hat OS virtualization experts.

Announcement: OSv, a new open-source operating system for virtual machines

InformationWeek, Charles Babcock: "Cloudius Takes On Linux as Cloud OS"

From the announcement:

Another refreshing feature of OSv is that is written in C++. It's been 40 years since Unix was (re)written in C, and the time has come for something better.

C++ is not about writing super-complex type hierarchies (as some people might have you believe). Rather, it allowed us to write shorter code with less boiler-plate repetition and less chances for bugs. It allowed us to more easily reuse quality code and data structures. And using newly standardized C++11 features, we were able to write safe concurrent code with standard language features instead of processor-specific hacks. And all of this with zero performance overheads -- most of C++'s features, most notably templates, are compile-time features which result in no run-time overhead compared to C code.