https://habr.com/ru/post/131581/
https://habr.com/ru/post/143402/

http://codepen.io
http://cssdesk.com
http://jsfiddle.net
http://dabblet.com
http://jsbin.com
http://www.sqlfiddle.com - sql
https://regex101.com/ - regex
https://dillinger.io/ - md (mrkdown)
https://3v4l.org/ - php

https://2cyr.com/decode/?lang=ru - Универсальный декодер - конвертер кириллицы

https://www.webpagetest.org/ - Test a website's performance

https://www.ssllabs.com/ssltest/analyze.html - проверка ssl сервера
https://caa.zilore.com/ - генератор DSN CAA записей

https://deepnudeonline.com