Portable bunkbeds? These are AWESOME. Great for grandmas House, a hotel room, or just a sleep over!
These things cost around $290 and up on Amazon, which is significantly more than a regular cot, which is around $40 (some smaller ones are a bit less). But the benefit of these is you save some space. For example, you might not have room to put to cots side by side in a living room, tent, hotel or wherever, or you might not want to carry two separate ones. Note though that these bunk bed cots also can be used as separate cots (they don’t need to be on top of each other). These things also have little storage pouches, which is something regular cots don’t have (not standard anyway; DIYers could certainly add them if they were handy).
And they convert into benches, the kind you might use camping or in your yard or the back of a pickup.
The main people who make these on Amazon are called Disc-O-Bed.