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Code Eval is several things.
Fast programmer's notepad
Quickly create notes and code snippets. They are stored locally, in your browser.
Create notes in plain text or markdown. Create code snippets in your favorite language.
A note can have multiple files. You get syntax highlighting.
A gist editor and manager
GitHub's gist service is great.
Code Eval offers a better way to manage and edit gists.
A code playground
Code Eval supports execution of code in multiple languages: Go, C++, JavaScript (via node.js). More to come.