Coyotos and Genode are two operating systems about which I had never heard that were mentioned in an Ikarus Users mailing list thread that doesn’t seem to have been mirrored online.
Coyotos:
Coyotos is a secure, microkernel-based operating system that builds on the ideas and experiences of the EROS project.
Genode:
We understand the complexity of code and policy as the most fundamental security problem shared by modern general-purpose operating systems. Because of high functional demands and dynamic workloads, however, this complexity cannot be avoided. But it can be organized. Genode is a novel OS architecture that is able to master complexity by applying a strict organizational structure to all software components including device drivers, system services, and applications. The Genode OS framework is the effort to advance the Genode OS architecture as a community-driven open-source project.