The Murphy, or foldaway, bed was invented nearly a century ago as a way to save space. This space-saving aspect of the Murphy bed is still appealing today, as the cost of housing drives many of us to live in smaller homes and apartments.
The traditional Murphy bed uses easily obtained special hardware, but there are other options too.
The head of a traditional Murphy bed is mounted against the wall, where it folds up and is hidden in a closet or cabinet. This is what most people think about when you mention a Murphy bed; even people who have never seen one personally have seen them in movies. (A classic example is the James Bond movie "You Only Live Twice," in which a Murphy bed is used to fake Bond's death.)
To build your own head-mounted Murphy bed, purchase special hardware that allows the bed to be easily folded up or down. The hardware comes with basic plans for a home-built enclosure, which you can customise to fit your own decorating style.
Side-mounted Murphy beds are becoming more popular, because they can be installed in areas where headroom is limited. Attics and other rooms with low ceilings are ideal for a compact installation using side mounts.
Again, commercial hardware is available to make building your own Murphy bed as simple as possible.
In many ways, side-mounted Murphy beds are more attractive to modern users than the more traditional vertical mounts. This is because they lend themselves to uses other than beds; they can also be used to create foldaway seating and lounging in entertainment areas.
Yes, you can have Murphy-style bunk beds. Just as trains and passenger ships have incorporated folding bunks for decades, you can do the same.
If you intend to use premade hardware, you will probably need to limit yourself to twin-size beds; otherwise, the top bunk may be too high for you to easily open and close. You will also need to provide some sort of support for the "legs" of the top bunk to rest upon.
If you choose to mimic the classic bunks of those old trains and passenger ships, you will not need Murphy bed hardware. However, you will need to make the bunks very narrow, perhaps three feet wide or less. You will need some sort of hardware that will allow the bunks to pivot up and down, and some ballast in the back edge of the bunks to counterbalance the weight of the bunk. A locking mechanism will insure that the bunks do not fold up unexpectedly. These sort of bunks are best suited to use with children, as they weigh far less than most adults.
And as with side-mounts, these techniques can be used for foldaway seating.