It is most likely an impact driver. Similar to what a mechanic uses to remove stuck nuts and bolts.

Check out the Milwaukee M18, (model #2601-22).
My son just got one and loves it.
Northern Tool has it on sale, with free shipping, now.
THIS IS NOT SPAM.

Here is a link that might be useful: Milwaukee Driver

They also come in 12V models that are incredibly powerful, but very compact. I've got the Milwaukee model 2401 and it's great. The lithium ion battery lasts a long time. I used it to drive about 100, 3" lag bolts into some studs and there was still plenty of charge left on the drill. You can get it for less than $100.

Panasonic and Makita also make nice 12V drivers.

Here is a link that might be useful: Milwaukee 12V driver

Thanks, looks like the right tool for my needs

It's called an impact driver and they excel at driving screws.

Everyone is going to have their opinion as to what is best and generally speaking you get what you pay for. Obviously a guy who builds decks for a living may have different requirements than a homeowner who is building one deck. Hitachi makes some very good tools at a reasonable price point. If you are looking for a professional grade tools, I would suggest looking at Tools of the Trade dot net (all one word). You might also look at the forums at the Journal of Light Construction (jlconline dot com). You need to be a professional to post questions, but anyone can read the messages and impact drivers are a regular topic of conversation.

"It's called an impact driver and they excel at driving screws."

Just make sure you have enough feed pressure if you are driving wood screws.

If the screw turns without going deeper it strips the threads being cut into the wood by the screw threads.

They are really designed for machine threads not wood screw threads.

They are really designed for machine threads not wood screw threads.

Huh? Unless I missed something we're talking about the cordless impact drivers available at any home center. Their primary purpose is to drive wood screws.

One still needs to apply enough force to prevent cam-out of the bit.

"Their primary purpose is to drive wood screws. "

Sounds like a good method to decrease the holding power of the screw.

Why not just drive it with a hammer?

Wood is not the strongest of materials, and if a screw requires that much force to drive the pilot hole is not sized correctly.

You are cutting threads ion to the wood as you drive the screw in.

High drive rates are well known to result in stripping of the wood and the holding strength (especially in withdrawal) is NOT going to be as good.

Nails are not even allowed to be used in withdrawal.

I think we are confusing two different tools. an Impact driver or Impact wrench applies torque only to a machine screw , bolt or wood screw. The impact is in a circular direction.
A driver drill or hammer drill rotates the bit with a fairly uniform torque and also aplies impact in an axial direction.
manufacturers and dealers as well as consumers frequently confuse these two different tools. I'm sure I'll generate some flames here claiming that I have the names or descriptions wrong. And maybe I do.

"an Impact driver or Impact wrench applies torque only to a machine screw , bolt or wood screw. "

The problem occurs if the feed force is not enough to match up with the rotation of the threads.

This is not as much of a problem with machine threads, but can compromise wood threads.

ANY rotation without driving force will strip the wood threads.

Thanks for all the input, The name of the tool, Impact Driver, is what I needed.