JSFiddle started as a little proof-of-concept app in 2009 by Piotr. Back then it wasn't called that, instead it was called MooShell, and it was made for the MooTools community exclusively – the only available framework was in fact MooTools.
Instantly, after showing his work to to the community, Oskar joined the project as interface and front-end developer. Shortly after, MooShell received its first redesign.
In 2010, a decision was made to make the platform available to every developer, of every framework, so JSFiddle was born, out of MooShell's source code.
Since then JSFiddle has been growing, there had been a few redesigns and many improvements. After 2014 JSFiddle had become so popular, major tech companies from the likes of Google, Facebook, Highcharts, Vue started using it for their purposes.
In 2016 a decision was made, to make JSFiddle the platform it deserves to be, at that point Oskar left the company he co-founded and started working at JSFiddle full-time, planning and hiring talent for a full platform overhaul. In 2016 a major interface and feature redesign was made, making it modern. The same year, JSFiddle became ad-sponsored, in order to keep the service running.