Scientific Linux is an unofficial clone of Red Hat Enterprise Linux

Scientific Linux is a recompiled Red Hat Enterprise Linux, co-developed by Fermi National Accelerator Laboratory and the European Organization for Nuclear Research (CERN).
Quote from the website:
Its primary purpose is to reduce duplicated effort of the labs, and to have a common install base for the various experimenters.
Tag usage
The Scientific Linux versions on Super User have the version number appended to the tag:
- scientific-linux-5
- scientific-linux-6
- et cetera
Links
- Website: https://www.scientificlinux.org
- Distrowatch: http://distrowatch.com/table.php?distribution=scientific
- Wikipedia: http://en.wikipedia.org/wiki/Scientific_linux