Rump kernels provide portable, componentized, kernel quality drivers such as file systems, POSIX system call handlers, PCI device drivers, a SCSI protocol stack, virtio and a TCP/IP stack. The fundamental enabling technology is the anykernel architecture of NetBSD, which enables the use of unmodified NetBSD kernel drivers.
Several platforms are readily supported, e.g. userspace (including Linux, Android, BSDs and more), the Xen hypervisor, bare metal (and by extension most cloud hypervisors) and the Genode OS Framework. Supporting an entirely new platform is a matter of implementing the high-level rump kernel hypercall interface.
The book Design and Implementation of the Anykernel and Rump Kernels describes the fundamental operating principles and terminology. Further technical information is available on the wiki pages for articles and publications & talks.