Title says it all, you can make a flowchart and run it in your browser. I hated it in school when we were just drawing these on a piece of paper.. Only later when we started with Pascal it kinda clicked to me.
It is mostly intended for teaching basics of programming. Used in lots of schools all around the world. Gets around 500 daily users.
There is a series of interactive tutorials: https://flowrun.io/tutorials
Also a free ebook: https://leanpub.com/learnprogrammingwithflowrun
Editor is open source: https://github.com/sacode387/FlowRun
Supports debugging, custom functions and recursion even.
This is an alternative to Flowgorithm, which only works on Windows.