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.
DROPS - The Dresden Realtime Operating System Project
L4 and Linux based research project aiming at the support of applications with Quality of Service requirements. At TU Dresden.
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]
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.
L4 Microkernel Family
Growing article, with links to many related topics. Wikipedia.
L4-based microkernel systems, for embedded systems to huge servers; Pistachio kernel. L4: tiny, fast, 2nd generation microkernel using hierarchical external pagers and guarded page tables. Goals: create, prove, establish new methodology for systems that helps manage growing complexity, minimize legacy dependence.
A secure platform for applications that use digital signatures. Based on L4 and Linux. Research project at Applied Data Security Group, Ruhr-University Bochum., Germany.
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.