Ed, I'd guess that the aqua socks are probably the closest thing to Fivefingers functionally that you could find. However, the big selling point of the Fivefingers is that they allow your toes freedom to move independently. You're not going to get that with anything else that I'm aware of on the market. Actually, I remember a long time ago that I believe Nike had a shoe where the big toe was separate from the rest of the toes but it wasn't the same as these and I'm not even sure if you can get it anymore (…or maybe you can – the Nike Rift…). Still, while this more resembles the Fivefingers than other shoes, I would question how functionally similar it is, especially with that thick midsole.
Steve, I would recommend a transitional phase to get to the most minimal if that's where you want to get to. Over time, we've weakened our feet and legs by wearing too much shoe. To go straight to minimal might overstress previously underused muscles, tendons, etc. and cause injury. A more gradual transition would allow your body time to adjust. That's my take at least and that's how I've been doing it.
That said, I never really thought of cross country flats. That would be an interesting next step for me to try. I almost got some aqua socks recently but, after trying them on, thought it might be too big of a transition from where I am now.