It started using Node.js; it switched to io.js in February. I think for the purposes of "What's the use-case for node.js?" node.js and io.js should be considered the same.
I think under this context, a student asking about node’s uses, drawing the distinction between io and node isn’t really relevant, especially since there are plans to merge the two.[1] But thanks for the link, didn’t know about Electron, seems really cool.
Nope, Atom it's based on electron[0] itself which use io.js and Chromium as a core.
[0] https://github.com/atom/electron