Whatever you want. A small selection of things I've personally written in Ruby to give an idea of breadth:
* The text editor I use day to day.
* A messaging middleware server
* A private cloud orchestrator (running ~1000 VMs across on-prem, a couple of colo's, managed servers and
* Many web application backends for various sites; e.g. e-commerce, CRM systems.
* Forecasting and simulation framework for a VC.
* Framework for statistical analysis of error rates for OCR engines, and models to attempt to reduce the error rates by applying various clustering methods (for my MSc; "dipped down" to C for kmeans a couple of other things via FFI; 95%+ of the lines of code was Ruby)
* Map-tile renderer (we rendered custom maps based on hundreds of layers of proprietary map data for customers) and the webapp to go with it (document managed linked to map data)
* FUSE filesystem doing on demand rendering and caching of the map tiles mentioned above for newly uploaded layers.
* Code to generate terraform files to deploy infrastructure.
And when I have time I play with writing game code using DragonRuby.
I can do all of this in a dozen other languages too. I've done in Ruby because Ruby is pleasant to use and feels most productive to me.
I think these 2 quotes by matz describe best ruby's philosophy.
> I hope to see Ruby help every programmer in the world to be productive, and to enjoy programming, and to be happy. That is the primary purpose of Ruby language
> Often people, especially computer engineers, focus on the machines. They think, "By doing this, the machine will run fast. By doing this, the machine will run more effectively. By doing this, the machine will something something something." They are focusing on machines. But in fact we need to focus on humans, on how humans care about doing programming or operating the application of the machines. We are the masters. They are the slaves.
> I hope to see Ruby help every programmer in the world to be productive, and to enjoy programming, and to be happy. That is the primary purpose of Ruby language
That's why I wish ruby to succeed but after 20+ years of the language being around and python is taking all the scripting needs outside of web, I'm not sure what area is left for ruby.
