Cygwin is a port of the GNU utilities (like bash, gcc, vi, openssh and many more) to the Windows platform. It can be used, for example to run a SSH server on your ReactOS installation. Current cygwin releases do not run under ReactOS but former (around 2016) do. Fortunately there is an archive.
To install cygwin on your reactos machine, proceed as follows:
Install firefox from the ReactOS Applications Manager
Download the cygwin setup from the mirror with firefox. (this is the 32bit version)
Start a cmd shell and navigate to the Download directory. Usually this can be reached by entering
cd "My Documents\Downloads"
Start the CygWin installer with the -X parameter (this disables signature checking which does not work with the archive).
To do so enter
(note that in cmd shell there is tab completion similar to bash)
Click Next until you reach the mirror sites.
as mirror. Be sure there is no extra whitespace after the link.
Click next until you can select packages
Add the openssh package (if you want to ssh into your machine)
Then click Install. Installation will take about 30 minutes
You have successfully installed CygWin under ReactOS. Coming up next we will show you how to configure the ssh server.
Reference: most ideas were taken from this site. Since XP is very similar to ReactOS many XP tips also work under ReactOS.