There are several repositories provided by CentOS and other 3rd party developers that offer software packages that are not included in the default base and updates repositories. While no list can be 100% complete, as anyone may announce an archive, it represents some major efforts and provides a summary of what each repository offers. These repositories have varying levels of stability, support and cooperation within the CentOS community.
Third Party Repositories
These repositories are not provided nor supported by CentOS.
Extra Packages for Enterprise Linux (EPEL). Provides rebuilds of Fedora packages for EL5, EL6 and EL7. Packages should not replace base, although there have been issues around point releases in the past. You can install EPEL by running yum install epel-release. The epel-release package is included in the CentOS Extras repository that is enabled by default.