Bicycle trail-along for twins

Hi --

I'm looking for the brand name of a tandem bicycle trail-along; one
of those devices that allows you to ride your bike with, not one but
two kids riding along behind you.

I've also heard them called Alley-cat (brand name), trailer bike,
and tag-along. Once or twice I've seen tandem ones, but can't seem
to locate a brand name online.

Any help out there?

Thanks,
- marty (mom to 5 year old twins)