Was this it? This is another option I liked and bought years ago. I still have it but found it didn't work as well as I wanted. The reamer was so big that the plugs would still leak. If you haven't seen these plugs, they're mushroom shaped:
the gun compresses the head and you shoot it inside the tire where it pops out and opens.
These are still sold under the "Stop-n-Go" name for use on motorcycles.
Unfortunately, these plugs simply don't work reliably on motorcycle tires. They should be called "Stop-n-Stay". The plugs eventually come out and end up bouncing around the inside of the tire. Maybe they work on cars, maybe not, but I doubt it. I don't see the point of carrying around a heavy tool to install vastly inferior repairs.
I've never had a "sticky string" repair fail on any vehicle. (Leaving aside situations where there's no safe way to repair because the hole is too big or in a bad place, of course.)
I'm surprised no one has mentioned Nealey Tire Repair kits yet:
http://www.tirerepairkit.com/
These are a type of sticky string, but they're installed in a different way where you end up with four strands in the hole (instead of two) plus a knot on the inside that keeps the repair from coming out. Plus, no added glue is required.
I've had EXCELLENT results with these kits, and they come in handy plastic tube containers.