I think this is greyzone, since it have android application which nobody shut down.
Some games can be downloaded here
I think Saya no uta is a good to begin with (short, only few hours of reading, small number of choices)
And you can google for converters if you are owner of a game and then its almost legal, if u dont mind that part about altering someone software.
Sorry for my language im not from english speaking country.