This adapter plugs into the back of an Apple II (all models with a DB9 connector on back, except an Apple IIc which also used the DB9 for mouse support), and splits out Player One and Player Two ports.  This was fully supported natively by the Apple II!

YES - The Apple II supported Two Joysticks natively.

Two X and Two Y axis' exist on the 16pin DIP connector and the DB9 connector on the back. Early on there was support for 2 paddles for up to four players. Only a few games support native 2 player with 2 joysticks. Archon 1, and Archon II support 2 player. One On One , Dr. J. and Larry Bird support 2 player and a handful of other games.

This board is simple to build, requires no logic chips, and for a few dollars you can build one.

Good luck and Apple II Forever !!

Video explaining how it works - https://youtu.be/N24VPiIjzCA