ctf sites

https://www.root-me.org/?page=news&lang=en
https://shellterlabs.com/en/
https://ctf.ritsec.club/login?next=%2Fchallenges
https://ctfs.me/
https://www.wechall.net/active_sites
https://ringzer0ctf.com/
https://www.hellboundhackers.org/

With VM + Challenges
https://www.hackthebox.eu/home
https://www.vulnhub.com/#

Write up and solutions
https://ctftime.org/
https://github.com/ctfs