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.
* 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.