Can anyone explain a bit more about what happened to Red Hat? I'm about behind the history of this Distribution. Last time I read about it I found out that is paid and I never considered it, because of that. I'm using Slackware for most of my servers, but I don't know what is the target market or what is more special in Red Hat Enterprise.
There are some misconceptions here. RHEL does not cost a cent. Support for RHEL, which includes security fixes through the package manager costs money. Security fixes and other patches and updates are still released as source by RHEL, as required by the GPL.
If you really wanted, you could run RHEL with no subscription and compile your own updates from the source that they release. In practice, this is next to impossible to maintain as an individual, but it is exactly what CentOS, Scientific Linux, and other related EL distributions do. They remove the RHEL trademarked logos, compile the code released by RHEL, and make it available through a generic yum repository that doesn't require a RHEL subscription.
So, in short, RHEL doesn't cost money, support and packaged patches do. CentOS gives you binary and version compatibility of RHEL without the cost.
It's been necessary to pay for RHEL for a while now. When you pay your subscription, you do get support from RHEL as well. However, if you just want to try the OS, you can go get CentOS. Since RHEL is open source, the CentOS team removes the RHEL name from everywhere and recompiles it.
One market that it seems to be strong in is the defense world, since RHEL is one of the few OS' that get various certifications for safety and security.
The biggest reason to get RHEL is certification (assuming you don't need their tech support or updates). A number of third party vendors will only support one of the Enterprise Linux distributions (RedHat, Suse, Oracle Linux, etc). Now the technical differences between RHEL and, say Fedora, is that RHEL gives you a long time of getting bug / security fixes that are "minimally invasive", that is you can apply them and have a very good chance that your existing configuration and apps still work without a reinstall ore reconfiguration. (This is what is meant by "stability").
For personal use, you can get similar stability from either CentOS or Scientific Linux, although the bug fixes will lag behind Red Hat by a few days (although some critical updates have been released only a few hours after Red Hat).
