What language was used to build DigitalOcean ?
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As alireza94 mentioned, our StackShare profile gives a decent overview of some of the technologies invloved in building DigitalOcean. At a very high level, we use Ruby on Rails for both this community site as well as our control panel. We also heavily use Ember.js on the control panel. Our backend services are mostly implemented in Go. Our homepage is a static site built with Middleman.
I think here is not the proper location for asking this question, But you can take a look at DigitalOcean's Stackshare profile.