What tools do you need to build a B9? The more the merrier. A table saw, drill press, hand drill, band saw, saber saw, disc sander and a Dremel are a must. A heat gun and soldering gun are also good to have.
There are some "gimmick" tools out there, some of which I've tried. You're better off using your basic shop tools and avoiding gadgets which usually yield less than satisfactory results. Some of them are listed below. Happy building!

The USB powered electric hammer

In theory it gives you a mild jolt of electricity facilitating involuntary hand movement in which to hammer objects without effort. Not only is this useless but you subject your computer to construction dust which is not good. Not recommended.
The Foot Powered Dremel

This is supposed to help you to use a Dremel roto tool if you don't have access to an electrical outlet. You have to somehow affix the foot pedal to something in the area where you'll be working. As it works on air pressure, you have to pump that thing like you're riding a bicycle in a marathon. Also the hose provided wasn't long enough to be useful. My advice is to either purchase a cordless Dremel for a few dollars more or get a long extension cord.
Hand Crank Disc Sander

This sounds like a good idea and had me sold by reading the many advantages printed on the outside of the box. However the design is awkward and I couldn't get enough RPMs going to make it work without getting a bad cramp in my hand. Not worth the $49.95.

Left Handed Screwdriver

"Solves all your problems when in a tight spot", that's what the advertisement said. The built in ratchet device and "special left handed bits" were totally useless to me, giving this a 0 on a scale of 1 to 10 in my opinion.

The Amazing Curved Drill Bit Set

When I saw this I thought it was too good to be true. It was. The set includes 32 various sized bits. It claims to be able to drill around corners, but when I started drilling with it, the thing just twirled around like a Roto Rooter snake gone wild, almost destroying the part I was working on. It almost wasn't worth returning to the bargain outlet I bought it from just to get my $2.95 back.

Gas Powered Hacksaw

This may work for a job where precision isn't required. I couldn't get the thing to cut a straight line within two inches of where I marked the cut due to the vibration. The thing is heavy and huge too, weighing 10 pounds and about 2 feet in length. Stick with the manual models that have worked well for many years.