Online Tools
For Java developers
https://jstack.review Analyze java thread dumps from within the browser. This page is client-side only. No data will leave your computer when you click Analyze.
http://gceasy.io/ Universal GC Log Analyzer
https://tryjshell.org/ Online java 9 jshell
http://codingutilities.com/substring Substring Helper
Network
DNS
https://www.whatsmydns.net/ DNS Propagation Checker
Get IP for domain in bulk https://www.infobyip.com/ipbulklookup.php
SSL / TLS
https://www.ssllabs.com/ssltest/viewMyClient.html Check client
https://www.ssllabs.com/ssltest/ Check server