If something is very successful, it doesn't mean it is very good and nothing can replace it. The world is currently divided into many school of thoughts, and only time will tell which kernel design is going to win the war. Also, there has been growing hatred towards Linux with its bloated kernel and eating all the RAM!
If anything is bloated, it's typical linux userland. The linux kernel, with uclibc, busybox, dropbox, and other userland tweaks, can fit onto an embedded router with 4MB flash and 16MB ram.
Linux caches in RAM pages of files it reads. It will evict them at the drop of a hat if it needs to.
Sadly, no matter how many blog entries appear on the subject, people still expect to see free ram, and think linux is bloated when they don't see any.
If you don't like that behavior, I don't know if any OSes leave "free" ram untouched. They might call it free though, even when it's used by the OS for caching.
On the issue of microkernels vs monolithic, I prefer microkernels for their elegance in theory. If one appears with performance in the ballpark of linux, that glibc supports and that will run linux userland with no problems, I'll switch. I will not, however, give up functionality in the name of ideology.
I'm given to understand that Debian and Arch linux have GNU Hurd live CDs out there for people who want to run it. I don't really know much about the OS, but does it meet your requirements?
If you're think of this as a Linux vs Minix 'war' then you are looking at it the wrong way. Minix is intended for research/education. Its not going to replace Linux because they do different things.
"It was only with the third version, MINIX 3, and the third version of the book, published in 2006, that the emphasis changed from teaching to a serious research and production system, especially for embedded systems. A few of the many differences between MINIX 2 and MINIX 3 are given here.
Going forward, we are making a serious effort to turn MINIX 3 in an industrial-grade system with a focus on the embedded market, especially for those applications that need high reliability and availability."
Okay, I wasn't aware of the Minix 3 redesign, so I stand corrected on that. Thanks for updating me!
But I'm fairly skeptical about how much use (if any) Minix is getting outside research and education. Aren't there already widely deployed HR/HA OSs that target the embedded market? What real advantages does Minix have over something like VxWorks?
I didn't intend to sound the way it seems i sounded. Sorry for that! Btw, the focus of Minix 3 has changed and it is no longer intended just for research/education. Minix 3 was publicly announced on 24 October 2005 by Andrew Tanenbaum and it is comprehensively redesigned to be usable as a serious system on resource-limited and embedded computers and for applications requiring high reliability.
Linus Torvalds' post to comp.os.minix newsgroup.