PetrOS® is a compact operating system which supports a very limited subset of the Win32 API.
It was originally developed by Trumpet Software International Pty Ltd, but has recently been acquired by Tattam Software Enterprises Pty Ltd.
The currently released version is 1.01, and is available for sale here
If you would like to try the demo version, a zip file containing the installation files is available here, and a README file to get you going. For ease of setup, a self extracting EXE of the zip file is also available here.
You will need a DOS bootable system to get it working as the installer runs from a DOS prompt, and also reset the date to 2001 as the this particular demo expired on 1/1/2002.
Please ignore any historic information about registration and support from the old trumpet.com.au site.
SHA1 checksums for the download files.