This came from a box of old computer equipment. It's two
boards joined together by stand-offs and several wires.
Only one of the boards has a bus connector edge.
Update from a reader:
It's a S-100 board, intended for the MITS Altair 8800. The bottom board
with the edge connector is a MITS serial board. The "TTL" designator
indicates that it does not shift the serial data to RS-232 levels. The
mezzanine board on top is an early modem board.
The large IC (COM2502) is a standard 40-pin UART. Look up the Western
Digital TR1602 for pinout and function. Quite a number of manufacturers
made their own 40-pin UARTs that, while having different pin names and
sometimes different speed capabilities, were almost always pin-compatible.
This is the "top" view. Click the image for a larger version.