The Toshiba HX-E600 is a slot expander designed for the Toshiba HX-10 computer series expansion bus.
It provides a second main slot (the bottom slot connector you can see on the top view picture, which is located at slot 2) and an extra I/O slot (the top slot connector you can see on the top view picture).
The product name is "Additional I/O Slot".
Note: This slot expander has no power supply of it's own, so it can't provide over 300mA (5V). Pay attention to the choice of cartridges.