Just saw this on slashdot, straight from the homepage:

"NewOS is a free operating system with full source code available, along
with periodic binary snapshots. Currently runs on:

Intel and AMD single and multiprocessor desktops
Sega Dreamcast "

"Implemented Features
Multithreaded
Multiprocessor
Fully reentrant
Protected memory
Separate user and kernel space
Text-based console
Full locking primitives
Object-oriented filesystem layer
Kernel debugging support with installable debugger commands


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Planned Features
Improved VM with memory mapped files support -- in progress
User space ELF loader
Realtek 8139 network card driver for Sega Dreamcast and Intel -- in progress
High-performance TCP/IP stack
Usable shell
Disk driver and disk-based filesystem
The list goes on...

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Current Ports
Intel IA-32 (x86) - Tested on desktops all the way to 4-way server
Sega Dreamcast - Hitachi SH-4


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Planned Ports
SGI Indy - MIPS R5000 based Indy in 32- and 64-bit mode -- in progress,
boots
Sun Blade 100 - UltraSPARC IIe in 64-bit mode
DEC Multia - Alpha
Amiga 3000 - M68040
Atari Falcon - M68040  "

Full source and documentation available - www.NewOS.org