What are some helpful websites and/or apps that are little-known to general public?

[19]

I have previously discovered some websites that I use now daily or weekly, like:
Sci-Hub.se - unlocks access to most scientific articles <website>
LibGen.is - pirated book library <website>
WinDirStat - shows memory used (visualized in graphic blocks)
Cracked.to - this is some really cool website I found some time ago, you should check it out for sure 

I will sure add anything I remember to the list.
I am sure there are more of these hidden treasures, the question remains:

What really helpful websites and/or apps do YOU know to exist?

Also please leave a like, that would be great ???

[611]

Subdomain Finder - C99.nl

finds subdomains, ik that tools like assetfinder exist but still it's pretty cool to just be able to goto a website

https://cracked.sh/Thread-⭐Editify-The-1...s-OP-Edits

[19]

I have also thought of:
Drawabox.com - completely free learning to draw courses, can almost be considered a university course
DareBee.com - well-illustrated website for workouts, workout plans, and challenges
MuscleWiki.com - Easy to use and understand workout planner, information and workouts for specific body muscles
GitHub.com/sindresorhus/Awesome - a repository containing loads of information on all kinds of topics, you have to check it out yourselves

[113]

Drawabox.com - completely free learning to draw courses, can almost be considered a university course

I need to check this out, this could be helpful.

I recently found a site that could decompile JAR files:
http://www.javadecompilers.com/