With 20 topics and around 100 training videos Google's Digital Garage is an excellent 101 of digital marketing. It is very 'SME', read "SE", focused and so seems to have a rather odd, either quaint or patronising, "nation of shopkeepers" flavour to it. 

But it has badges and a certificate! And much as we might prefer that it wasn't true, we know that gamification works wonders.