Ethical hacking platforms/trainings/CTFs:

http://crackmes.one http://ringzer0ctf.com http://pwnable.kr http://ctflearn.com http://domgo.at http://pwnable.tw http://tryhackme.com http://ctfchallenge.co.uk http://cryptohack.org

Source: https://twitter.com/trimstray/status/1262985978618281986