Well, it's got something to do with television or video processing. The boxes for NTSC and PaL imply that. Also, there's a bank of VRAM labeled "Frame Buffer" so presumably it can work as a video card or drive a television type monitor as well. It looks like it used to have some kind of break-out box that connected to the connector on the end of the card.

I think "Digital F/X" was the name of a company back when? You might try googleing on that term.

Here's a very short magazine article which refers to the company:

http://www.accessmylibrary.com/article-1G1-9772185/digital-fx-takes-video.html

Mountain View, Calif. -- Digital F/X Inc., which made its entry into the Mac market last year with an on-line desktop video editing system, last week introduced software for off-line video editing.
Soft F/X, a $995 program due in April, does with software what the $9,995 Video F/X system does with hardware (see MacWEEK, July 31, 1990). It lets users edit and organize video and audio clips into a presentation.

Click to expand...

So, presumably, the July31, 1990 article would discuss the hardware you probably have there.

Interesting. That port on the top of the card looks like it would use a cable to connect to the DAV port on the Power Mac AV card (which has the exact same type of connector)