Microkernel

A microkernel is an operating system that concentrates on pure minimalism while still delivering contemporary operating system features. The basic idea is to include only those things in the kernel which cannot be provided from user-level services. All other features, such as device drivers and application memory managers, are all user-level services -- just like the webbrowser you're using now.

See http://www.l4ka.org for more information on one particular kind of microkernel, and my personal favorite: L4. -- Samuel A. Falvo II