Ast I∕O Plus II
The Ast Research I∕O Plus II is a serial/parallel/gameport board.
Socket U4 is optional, and can be populated with a compatible UART to provide a second serial port. In the main photo a Winbond W86C250B can be seen here. This is an equivalent part to the INS8250N-B providing the first serial port. Both these parts are 8250-compatible UARTs.