Reverse Domain Lookup Sites
http://www.webtoolhub.com/tn561350-reverse-ip-domain-lookup.aspx
http://get-site-ip.com/
https://ipaddressguide.com/dnslookup
Other Guilds
https://github.com/rmusser01/Infosec_Reference
An Information Security Reference That Doesn't Suck https://rmusser.net/docs
https://github.com/kbandla/APTnotes
Various public documents, whitepapers and articles about APT campaigns
DevOps
https://github.com/sovereign/sovereign
A set of Ansible playbooks to build and maintain your own private cloud: email, calendar, contacts, file sync, IRC bouncer, VPN, and more.
Malware
https://github.com/IAIK/meltdown
This repository contains several applications, demonstrating the Meltdown bug. https://meltdownattack.com
https://vx-underground.org This site houses code samples and APT information.