Hi,
I will maintain a C program which I was told it should only work on Redhat Linux. I want to setup a development environment for it but I'm wondering if Redhat Linux server is free? If it's not free, is there any other free Linux distros can relpace Redhat for me?
CentOS takes the source code, and files off the 'RedHat' trademarks.
'Free' is a more interesting question - as the word is overloaded in the English language. No cost, vs freedom. CentOS (and some others) are made to be binary compatible with RHEL and each other - only the copyrighted work of Redhat has been removed, or possibly replaced where appropriate.
According to their download page, RedHat Enterprise is not free.
Wikipedia has a list of RedHat derivatives distributions. If a distribution is binary compatible with RedHat, your program should run no problem, even if just installed using the .rpm.