You can download the game but when you launch it, there is a pay-and-entree wall or the option to play a demo stage. This is not a public build!

The reason why it asks for a code is to prevent pirating the game, To "Purchase" the full version you need to just subscribe to their patreon (Not recommended) or ask literally anyone for the code to the game as people are more than willing to just give it out because Jasonafex just.. doesn't deserve the money, 
The code for the most recent version is 9175.