Pong
Pong is a game commonly used to teach new Scratchers how to use Scratch. AngieJones made a pong game called Pong Easy Bro in 2017, which became frequently referenced amongst the remixers.
Pong projects
Pong remix tree
Related projects
Pong in the remix tree
(There's also r/snapple:) and its remices, but those become increasingly less game-like, and so it's diminishing returns to include them here.)