Hello Birde,
I do plan on adding an HTML browser version. For mobile it has not been planned yet, but it will surely come after the HTML release.
Right now the current world select screen is a concept I have plans to change it to something more impactful than a list, such as a book which fits nicely into my theme of a novel-like game. In other words, this is a concept idea with no functionality to it and no gameplay. I am quite glad that you were able to understand the "available" button because I believed that it was too confusing for players therefore I have changed it into something else I am much happier about. My plans are that anything before ver 1.0 is just a concept where I am greatly changing how my game works on a fundamental level to see what works best through trial and error. By v1.0 I plan on having a fully working world (1) where you can play as a character.
TL;DR - It supposed to not do anything as I have not yet worked on the world itself + I didn't really enjoy how it appeared, therefore I have also changed the appearance to something more fitting with my theme.