itch.io

The game can be anything you like, so long as it fits the theme (I'd personally love to play a battleship-like game). As for whether it's allowed, it being a paid software and all, I had the same confusion since I'm using RPG Maker which is paid too, but everyone who answered told me it should be fine, because it's not like anyone can have access to the software itself from your source code. I'd think yours is a similar case to mine, so I think you should be all good too :)