Here is a download for my TinyBlocks game for Arduboy. It is one of the very few greyscale games for the system as the screen is only capable of showing one colour.
The effect is achieved by flickering the screen as fast a possible so that the image of some of the pixels is retained while the next ones are drawn, a little like this –
Which on the small oled screen should look a bit like this –
Download tinyblocks 4.45k