Press the green flag. In the overworld, use the arrow keys to move around. In battles, use the mouse to select actions.
Yeah, this came out of nowhere. I started working on it a few months back, but I just forgot about it. Most of the overworld engine was done by the time I came back, but not much else. Other than that, feel free to use the engine! (with credit) UPDATE 1/3/18: Sped up the attack animations, and turned down the encounter rate.