While I haven’t put it in the traditional stacks, I’ve “harvested” hay from areas that haven’t been fenced in yet. Yes, it is a lot of work, but it does help the hay budget.
I’ve done it two different ways…
If the grass wasn’t terribly high, I’ve used a riding mover. I would run a bare swath down where I would want a windrow, then mow both sides of the windrow area to spit the grass into the bare place. I raked the windrow up neatly, flipped it as needed until it was good and dry, then scooped it onto a wagon to store inside. Or, if I knew it was really really dry, I’ve stuffed it into paper feed bags or something that it could breathe a little bit and stored it under shelter.
The other way is using a brush hog, then rake and dry like above. That year I had a large space inside one corner of the barn, and stored it all piled up.
Can’t say that “making” hay this way is my favorite to do though, and I haven‘t done an area bigger than one acre at a time.
I will say that I've used this homemade hay primarily for my non-horse farm critters though, and I've utilized the bagger feature on my push mower more than once to help put all the cut grass to good use.
(disclaimer: there have been no chemical based products used on any of my grass or fields, and only natural or organic anything else.)