I can't see how it could be a zither....are those "nubs" big enough to attach strings?
Looks like it's part of something....like a shelf support.

Yes, I think they could have strings attached. Here is another pic:

Well, put it inside so the paint doesn't fade more!

How big is it? It does have the heavy duty stringed instrument vibe, doesn't it?

The thing that is against it being a musical instrument is that it is cast iron. Which means it is heavy and most musical instruments would be of a weight to be carried easily. If you look at most musical instruments they either reflex the sound or mute it and cast iron does neither. I agree that it was part of a seat however in the picture to me it only appears that the scroll work is cast iron. When I first saw the picture I thought of a 1920s movie house seat. The rows of what appear to be the remains of nails does have me puzzled.

Edited to ask if a picture of the other side could be shown.

Ever see the inside of a piano.....and what the strings are attached to? Cast iron!
Looks like it could be part of a stringed instrument....missing some parts, likely wood taht would provide resonance....and some place to attach the other end of the strings.

Well, Linda, you don’t hold a piano, you attack it ;) with feet and hands.

Part of a square grand?

Some zithers have legs and are played almost like a mirimba.

The decorations (painted and cast) suggest that the painted side was meant to be visible, so I doubt it was inside a piano.

The insides of many pianos are very much intended to be seen (and we don't know if the paint is original, although many are painted). The one pictured above is decoratively cast and gilded ( and in the Smithsonian). Here is a similar one that isn't all shiny:

I was thinking the same as others here - that it's from the inside of a piano, harpsichord, clavichord, or similar. Many things in the past were embellished with very ornate patterns even in areas that might not be easily or often seen.

I found a pic similar to Fori's in a square grand and the shape sure looks similar to the op's:

I'm not familiar with piano guts. But this thread is interesting and I want to note it for later :)

Yup. Piano guts. But not a modern piano. Even the square grand Oly posted is probably later than the one that donated the part in question--it has extra those bridges on the keyboard end. The simpler ones were more mid 1800s. (Before that there wasn't enough tension in the strings to warrant cast iron plates. Wood was adequate.)

Maybe the rest of it is a desk somewhere. They were always so pretty.

Is it a Zither like this one? Zither Albert Sommer about 70 years of age