OSv is written in C++11 and designed to run on KVM, Xen, and Amazon EC2 instances while there isn't yet support for VMware or non-x86 architectures. OSv strives for superior performance, zero OS management, a common Java framework, an optimized JVM, and other common cloud workloads. While not powered by the Linux kernel, OSv is said to be compatible with existing Linux programs and run-times.
For those wanting to dive deeper into this new cloud-only operating system, there is a mailing list announcement, the code is on GitHub (and there's also sample QCOW2 images), and a lot more information to be found at OSV.io. The presentation slides from the CloudOpen announcement can be found on Google Docs.