I would just like to help clarify the Egyptian ability, by taking it to as simple as I have had to for some people I have played with.
During the City Management phase of the turn, Egypt may select any one city they own that is using production to build a building, to instead build the building for free.
This may be used every turn, but for only one city per turn.
Now, for the sticky part.
Are wonders buildings?
On a read through of the rules, there are two things to consider:
1) wonders are not merged with buildings, when something applies to both building and wonders, both are mentioned. ie: overbuilding.
2) wonders are built through the same city action as buildings... and figures and units.
Based on that, my group has been treating wonders as not buildings, and therefore Egypt may not free-build a wonder.
Egpyt must build wonders in the same way as all other civilizations... find a way to generate enough production at one city to afford the wonder desired.