Closest thing to Red Hat Enterprise Linux 7?

As mentioned in the previous question, CentOS is your best choice since it is derived from the sources of Red Hat Enterprise Linux (RHEL).

Also as mentioned in their Technical and Release notes, almost all your required tasks are met in CentOS.

If you qualify as a "developer" you may be able to get genuine RHEL for free, subject to usage restrictions (basically, "no production usage")

https://techreport.com/forums/viewtopic.php?t=117614

ISTR there was also a RHEL student edition, but I'm not sure if it still exists or what is its definition of a student. It wasn't free, just cheap.