Parknav is described as 'uses artificial intelligence to know where there is open on-street and off-street parking in real-time'. There are three alternatives to Parknav for iPhone, iPad and Android. The best alternative is Parkmobile, which is free. Other great apps like Parknav are SpotHero (Free) and Prked (Free).
SpotHero's website and app (iOS & Android) helps drivers find, compare, and book discounted parking in lots and garages in major U.S. cities including Chicago, NYC, Boston, Baltimore, Washington D.C. and others.