tldr; light weight Visual Studio for OSX/Windows/Linux with support for dozens of languages, intellisense (autocomplete), refactoring, debugging (yes, real debugging) and it is free.
"free" as in "beer" or as in "speech"?
Wasn't specified, so I'll conservatively say 'beer'.
It's free as in XCode.
It appears to be a fork of Atom.io. Just take a look at the app contents on OSX.
$ ls "Visual Studio Code.app/Contents/MacOS/"
Atom