Recreational use of marijuana was legalised in Colorado and Washington in 2012. Alaska and Oregon made it legal in 2015, with more US states - especially those where it is already allowed for medical reasons - expected to follow. And where legalisation leads, opportunities to make a lot of money follow.
A number of tech startups have already started to take advantage of this vast (and growing), multi-billion market for cannabis products. They include Uber-style delivery platforms, review and information websites and social media for stoners.