Does anyone know what this hose is? It’s just laying in my engine bay

 

cruise control

 

As stated above, it's the vacuum line for the cruise control unit.

 

But where does it attach? (My car doesn't have cruise).

 

That's the vacuum source for the Cruise Control diaphragm valve located at the top right of the pic above. That canister thing with the cable coming out of it and going to the throttle linkage is the remote actuator. It needs vacuum from the intake to pull on an internal diaphragm to adjust throttle position; as more vacuum is generated (*going uphill, under load, etc.), that vacuum source applied to the diaphragm pulls on the cable, making it a variable cruise control to match load conditions.

The hose attaches to a barb on the intake manifold, under the carburetor.

 

On 85 at least, it connects to the rats nest, an upward facing barb at the rear between the carb and purge valve. If you've deleted the cruise control box behind the driver's seat, just remove that hose, and the large actuator and throttle cable it was attached to.