The 3DO BT is a Bluetooth Adapter that allows you to connect various Bluetooth controllers to your 3DO. This includes PS3, PS4, PS5, Xbox One, Xbox Series S & X, Switch Joy-Cons, 8BitDo (Bluetooth only) and other Bluetooth controllers.
The 3DO BT runs on the incredible BlueRetro platform by Jacques Gagnon. A portion of each sale is donated to Jacques to further support the platform.
Note: Bluetooth is limited to 7 device but there is a way to connect 8 devices using a Wii remote and BlueRetro mapping as explained here by Jacques Gagnon.