The names in the parentheses denote the symbols to be used for static linking of the drivers.
No graphics drivers are currently available for the Plus/4.
No extended memory drivers are currently available for the Plus/4.
Supports up to two joysticks connected to the standard joysticks port of the Plus/4.
Currently no drivers available (in fact, the API for loadable mouse drivers does not exist).
Driver for the 6551 ACIA chip built into the Plus/4. Supports up to 19200 baud, hardware flow control (RTS/CTS) and interrupt driven receives. Note that because of the peculiarities of the 6551 chip transmits are not interrupt driven, and the transceiver blocks if the receiver asserts flow control because of a full buffer.
You need an adapter to use the builtin port, since the output levels available at the user port don't follow the RS232 standard.