The Flash Player itself is not Open Source, though many of the related technologies are.... While fully possible, it's not a trivial thing to create your own Flash Player. Creating just the simplest player that supports a tiny subset of features is hard enough and the Gnash project is the only active effort we know about. This is not because Adobe prevents others from creating their own Flash Player, but rather since it's not a trivial thing to do. In blog comments all over the web, you'll find anonymous trolls that post comments saying that "Adobe's Flash Player sucks", "the Flash Player has a rotten code base" and so on. It's very easy to make such bold statements when you never even read the spec or tried to implement it yourself.