Genode OS: A tool kit for highly secure special-purpose operating systems

The Genode OS Framework is a tool kit for building highly secure special-purpose operating systems. Genode is based on a recursive system structure. The framework provides mechanisms to let programs communicate with each other and trade their resources, but only in strictly-defined manners. In line with Unix philosophy, Genode is a collection of small building blocks, out of which sophisticated systems can be composed. But unlike Unix, those building blocks include not only applications but also all classical OS functionalities including kernels, device drivers, file systems, and protocol stacks.

Source: genode.org