This is definitely from an embedded browser in an Electron app (electron.atom.io). Electron lets you create cross platform applications using web technology (HTML, JavaScript, CSS etc), and it also lets you embed a web browser interface, which is what this appears to be from.
This particular user agent has both an "Electron/1.0.0" fragment as well as an "Electron/1.4.3" fragment.
We've seen this user agent tens of thousands of times, so it doesn't appear to be a single developer making a mistake with configuring their user agent, but rather something native to Electron. If any Electron developers can shed some light, please get in touch.
We see developers do some strange things with user agents sometimes; our hunch is that it might be there to show that it's a "1.0.0" branch of Electron (in case some websites scan for that specific user agent, without doing proper version checking), but then it also includes the actual version number: 1.4.3...