I have had a plan in mind for over a year to make a folding router table to attach to one end of my rolling shop table, and at the beginning of March I finally made it. I bought a second router with a burned up motor on eBay and attached the base to the bottom of an 18" square piece of 3/8" 6061 aluminum plate that I got on sale from Online Metals last January or so. This way I can use the router motor either in the table or in the regular base.
I used two door hinges and some scrap wood to attach the table to the end of the shop table, and I arranged it so that when the router table is folded down it is below the level of the adjacent tabletop, and when it's horizontal it's just a bit above it. Then I took another hinge and another piece of wood and made a support arm to hold the table in level position, which swings 180 degrees out of the way when the table is folded. The arm feels quite solid, though I wouldn't want to try to sit on the router table. I mostly use the router for certain steps when making banjos and guitars, so the parts I am routing rarely weigh more than a couple of pounds anyway, and even on the rare occasions when I am making furniture the pieces I have had to rout aren't very heavy.
To put the motor in and out I can swing the table up past vertical and it will stay there by itself. I use the router table either with pilot bearing bits or with jigs, so I never need a miter slot, and I can attach a straight board to the table with clamps if i need a straight fence. My old router table was one of those little Craftsman ones that you set on top of the workbench, so this is a big improvement for what I do. I now have room to more easily fit the spindle sander, small belt sander, and scroll saw on the lower bench, without the old router table having to squeeze in there too. The only downside is that this router has a much better fan then the old Craftsman, so it blows shavings and dust up into my face if I stand in the wrong place. I will set it up for dust collection one of these days.