I understand Duotone is processing a patent for some element of the full boom. It might not entirely prevent others from doing something similar, but it will limit the implementation. As such, there really aren't any other full boom alternatives that I am aware of.

Vayu has launched a foldable multi-boom concept that could be worth looking into (very new to the market, so not a lot of availability or reviews).

Cabrinha also has mini boom handles on the Crosswing and the Mantis. It is a rigid handle that allows for a good bit of hand movement, but it doesn't have the rigidity of a full boom.

Some people fashion their own booms to span conventional loop handles (for instance the Armstrong boom extender).

Thats all that I know of, but I might be overlooking someone.

The Cabrinha Mantis has two "mini-booms" and there are a couple of others but probably tough to find. Check out this thread:

www.standupzone.com/forum/index.php/topic,36848.0.html

Eleveight recently released a boomed wing too. I know nothing about it though.

www.eleveightkites.com/wings/wfs-v2

ENSIS will come with a boom