Amiga OS 4.1

[KimmoK]

@mistermsk;
>did they just build off of Linux (like ArOS)?  

AOS4 uses re-implemented exec kernel and it's source code is ported and improved from AOS3.1.
Here you can see how AOS source code has been developed during the last 25+ years:
http://hyperion-entertainment.biz/index.php?option=com_content&view=article&id=141:twenty-five&catid=36:amigaos-4x&Itemid=18

> if I wanted linux tools...

Linux tools have been ported to AOS4 because it has been possible to do to make AOS4 SW offerings more complete.

Here is one example what SW you can use on AOS4:
http://www.blitterwolf.com/testing.html

Most new (AOS4 original) and ported SW can be found here:
http://os4depot.net/

New and updated SW is released daily:
http://os4depot.net/index.php?function=recent
http://aminet.net/recent  (notice that most 68k Amiga applications can be run on AOS4 as well, +AOS4 comes with AOS3 files for emulation needs)

For new AOS4 user, this document is nice starting point for the search of SW:
http://www.os4depot.net/index.php?function=showfile&file=document/tutorial/gtmooya2011.pdf

To sum up: perhaps 1% of available AOS4 compatible Application SW is ported from Linux/Unix.