L4 Microkernel
L4/MIPS: stable L4 for MIPS R4x00 processor, may be fastest kernel for this architecture. L4/Alpha: begun at Technical University of Dresden, SMP version released. Linux ports: L4/MIPS, L4/Alpha underway. You Would also find info related to operating system microkernel, 64-bit operating system, L4, open source, free software, operating system internals documentation, inside operating system microkernel and much more.

SawMill: A Highly-Configurable Operating System
Goal: address the complexity of building and maintaining a variety of custom OSs. As embedded and personal systems grow more common, the need to make OSs customized to many device and application needs rises. At IBM T.J. Watson Research Center.

The Hurd on L4
Porting the Hurd to the L4 microkernel. News, plans, pointers to mailing lists and websites.

Fiasco
Preemptible, realtime, 2nd-generation microkernel, fast, maintainable, readable, supports hard priorities, uses non-blocking synchronization for kernel objects to guarantee priority inheritance, ensure runnable high-priority processes never block waiting for lower ones; rework of L4 interface. [Open Source, GPL] You Would also find info related to microkernel, µ-kernel, fiasco, l4, l4linux, operating system, drops, hohmuth and much more.

L3-L4 Microkernel Family
Lean, with fast, message-based, synchronous IPC, simply-used external paging mechanisms, security mechanism based on secure domains: tasks, clans, chiefs. Kernels try to implement only a minimal set of abstractions on which OSs can be built flexibly. L3 has system-wide persistence. You Would also find info related to microkernel, µ-kernel, fiasco, l3, l4, l4linux, operating system, drops, hohmuth, liedtke and much more.

L4Ka Project
L4-based microkernel systems, for embedded systems to huge servers. L4: a tiny, fast, second generation microkernel using hierarchical external pagers and guarded page tables. Goals: create, prove, establish new methodology for systems that helps manage growing complexity and minimizes legacy dependence. You Would also find info related to operating system, operating systems, distributed systems, real-time systems, kernel, microkernel, microkernels, l4, l4linux, linux, sawmill, memory, memory management, cache, caching, virtual memory, file system, IO management, thread, threads, process, and much more.

Perseus
A secure platform for applications that use digital signatures. Based on L4 and Linux. Research project at University of Saarbruecken, Germany. You Would also find info related to practical security, l4linux, perseus, trusted applications, mobile security, microkernel, µ-kernel, fiasco, l4ka, secure environment, e-commerce, online banking, home banking, secure operating system and much more.

SourceForge: L4Ka Microkernel
The L4Ka microkernel is an L4 compatible kernel running on many platforms: ARM; MIPS; 68k, PPC; x86. A port of Linux atop an L4Ka microkernel exists.