SPIN  
   Dynamically extensible, Exokernel-based, provides many core services: scheduler, kernel threads, domains, event dispatcher, security mechanisms, primitive VM operations. Blurs distinction between kernels and applications, which traditionally live in user-
   http://www.cs.washington.edu/research/projects/spin/www/

Using Kernel Extensions to Decrease the Latency of User-Level Communication Primitives  
   Suggests solving networking and distributed systems latency via operating system extensibility; University of New Mexico Technical Report.
   http://www.cs.unm.edu/~riesen/prop/

SPIN: Extensibility, Safety, and Performance in the SPIN Operating System  
   Presents an extensible OS based on MIT Exokernel that can be dynamically specialized to meet the needs of individual applications.
   http://http.cs.berkeley.edu/~gribble/osprelims/summaries/SpinOS.html

VINO  
   Extensible OS, high reusability and modularity, application-directed kernel policy, universal resource interface, take no usual solutions for granted (question everything): software and postscript downloads.
   http://www.eecs.harvard.edu/~vino/vino/

Synthetix  
   Extensible technology for adaptive systems: researching tools, techniques to incrementally specialize OSs to optimize performance, meta-programming languages to let applications declare specialization needs to OSs, and to specialize distributed systems to
   http://www.cse.ogi.edu/DISC/projects/synthetix/

Extensible Operating Systems  
   Brief description, and on-site links to descriptions of Choices, Exokernel, GLUnix, VINO, SPIN.
   http://www.cs.unm.edu/~riesen/prop/node26.html

A Caching Model of Operating System Kernel Functionality  
   Stanford Cache Kernel, supervisor-mode component of V++ OS; caches system objects (threads, address spaces) to raise performance; microkernel alternative, performance equals normal monolithic OSs, yet gives application-level control of system resources, m
   http://www-dsg.stanford.edu/papers/cachekernel/main.html

BITS  
   The Component Based Operating System: based on describing system resources as independent components, lets applications implement their own abstractions, define their own protection schemes, participate in resource management.
   http://www.soi.city.ac.uk/~patty/bits.html

Open Kernel Environment: OKE  
   Lets non-root users load native, fully optimized code in kernels. OKE Corral: active network environment, lets 3rd-party code manage code organization at any level of nodes. LEGO-like model from MIT Click router. Description, papers, release page, contact
   http://www.liacs.nl/home/herbertb/projects/oke/