Where that icon on my OS X menu bar comes from?
I don't recognize the icon, but I may have a way to find out which app it belongs to.

Bartender is an app that organises the menu bar apps, but can also show which apps are already there.
It's a paid app, but you can install the trial, find the mystery app, then uninstall Bartender.

A screenshot from an installation of mine.


Tip: If you just want to remove the icon you may be able to ⌘-drag it away from the menubar, but for that to work the app needs to be an Apple built-in app or use the same menu bar hooks.