Is there a free, super simple app or website for IUPAC names from structures?
A bit more intuitive to interact with may be Chemdoodle Webcomponents which is a JavaScript library set-up to integrate well within webpages and mobile devices like phone or tablet, too.  It comprises 2D/3D sketcher, a NMR predictor, and is freely available (open source GPL license).  Derived from Chemdoodle, there is a structure -> name utility speking multiple dialects (e.g., IUPAC / CA, Hantzsch nomenclature), too.

Example:


The interaction with Chemdoodle is nicely explained by Pritt Balagopal here on ChemSE.