The overall "theme", in fact, seems to be something to do with travel, with each sim being named after, well, some way of getting from place to place. I started out in the FFL Journey sim, which looks like a sort of Steampunk 1900s New York, lots of brownstone tenements and odd steam-driven vehicles in the streets.
Then, looking out from the edge of the sim, you see the next one, FFL Trek, which appears to be an airport.
It has a mix of quite modern equipment with some old-fashioned modes of transport, and some rather fab art-deco style terminal buildings. We all know I'm a sucker for art deco, right?
Moving on, the next sim is FFL Parade, which isn't quite so transport-y, being largely a winding path between ancient stone temples, with a water feature in the middle. There are airships and tricycles, though, as you can see.
It's all rather nice, really.
Anyway. Those are the three I've been to, so far. I will be hitting the others, in part because I'm doing the passport game which Lindal mentions in her post. This involves getting a passport HUD and then acquiring a "souvenir" item in each FFL sim which gives you a stamp on it. Collect a full set of ten stamps and you can claim a free prize. So far, my souvenirs comprise a kid's tricycle, a teddy bear holding an aeroplane, and a rabbit with a helicopter rotor on its back. Well, that's SL for you.
I will observe, by the by, that the sims were rather quiet when I visited them. This is a shame. They are good builds, with good shops, for a good cause. They should be busier than that! Get out there and shop, dear readers.