Release Candidate versions are available in remi-test repository for Fedora and Enterprise Linux (RHEL / CentOS) to allow more people to test them. They are available as Software Collections, for a parallel installation, perfect solution for such tests. For x86_64 only.
RPM of PHP version 5.6.21RC1 as SCL are available in remi-test repository for Fedora ≥ 20 and Enterprise Linux ≥ 6.
RPM of PHP version 7.0.6RC1 are available as SCL in remi-test repository and as base packages in the new remi-php70-test repository for Fedora ≥ 21 and Enterprise Linux ≥ 6.
As PHP 5.5 is now in security mode only, there is no more RC.