Caret the Chrome App vs. Caret the PC App -- not sure which came first, but they are very different (except for the name, and the fact they are open source).
Caret the Chrome App
Caret the PC App (Linux, OSX, Windows)
Note that while Caret the Chrome App may possibly replace Atom, Caret the PC App has some great built in Markdown display (it is Markdown-focused rather than general-text-editor-focused). - Caret.io website - Caret on Github - Caret wiki on Github - Caret on Twitter