The popular social trading site TradingView uses a language called PineScript for creating indicators (that you can plot very easily) and strategies (that can be backtested directly on the platform).
Here are links to some resources for getting started with TradingView & PineScript (mostly for my edification when I get back to this):
- PineScript Tutorials on YouTube from the Art of Trading: Also here.
- Udemy Course: Learn TradingView PineScript Programming from Scratch
- Another set of PineScript Tutorials on Youtube
- Great Intro to the TradingView UI
TradingView itself has some great documentation. And another great resource is Kodify.