[cferr]

Since it hasn't been mentioned yet, I'll throw in Nagios. Having had to roll and maintain an in-house solution with similar functionality before, Nagios is a huge breath of fresh air.

Red Hat Enterprise Linux 7 is also awesome. I wish we could have 8, but that's not quite in the pipeline yet. The distro is crazy stable. With the Extras, Optionals, EPEL, etc. repositories enabled you get access to almost all of the best software in the Linux ecosystem.

Ansible, particularly Red Hat Ansible Engine, is also amazing for managing all of my Red Hat servers. I couldn't imagine doing half of my job by hand, as nothing would ever really get done. With Ansible you just fire off a playbook and relax.