This protocol for fair cake division works, but only just, for more than 2 people:

• Nominate one person, the "slicer" (there is no advantage in being the slicer).
• While more than 2 people (including the slicer) are still waiting for their slice, the slicer slides the knife from right to left along the cake. The first person to shout "stop!" gets the slice of cake cut at that point.
• Now just 2 people (the slicer and another) are left; they use the 2 person fair cake division protocol.

Note that if each participant is supremely egotistical, none of them can complain: each of the non-slicers cannot afford to wait for a piece larger than an equal share (else she risks another one of the non-slicers cutting in, and getting more than her fair share). And the slicer is assured by this that all pieces are equal, hence he's not cheated, either.

Of course, problems start when if you assume that coalitions are allowed. In particular, the non-slicers can gang up against the slicer, and by cooperating get each more than her share. But that requires a certain degree of cooperation, which is usually not assumed in cake-sharing situations.