While all of its features, taken separately, are available for free, CodeRunner makes it painless to sit down, choose your language, and just start coding.
We believe these characteristics are what it takes — not just to develop good code — but to create great products, satisfied customers, and happy users.
I just went through the practice of speeding up a large JavaScript test suite for my project. Here are some of the culprits I found and how I fixed them.