Low-friction brake calipers
 

Is there such a thing as brake calipers that pull away instead of DRAG on the rotor? it seems like a wheel that spins more freely (with less friction) will require less work to rotate and thus, save gas.

Yes.

that is how most calipers are suppose to work but you probably get closer to it working well in only 2, 4 etc piston calipers were there is opposing pistons on both sides as floating calipers don't always stay floating properly.

The piston seal is square and is suppose to retract back when brake is not applied .

There are 3 things I know of used to ensure the brakes drag.
1 hardware, spring holders, nuts and bolts were added to calipers and pad backing to retract them. But the set up needed to be adjusted constantly.
2 On newer vehicles some engine vacuum is applied to the braking system some how to help remove brake drag from the rotor at highway speeds.
3 put properly functioning drum brakes all around.

Yes, many vehicles add V or Z springs between the pads to keep them off rotor .Thes springs are not strong so there only for the pad, not the pistons as they should do it by themselves .
And , right all the hardware needs to be keep lubed. the inner pads on many back brake housings get rust, crude that stops them from moving correctly .

Remember that you also have to make up for that pullback with increased initial pedal throw. GM had some cars with these calipers with increased pullback but I think the master cylinders were matching too.

FWIW, my front calipers went from medium dragging to near zero dragging by eliminating the anti-squeal goo I always used to use (the orange/red stuff by CRC), and eliminating the shims.

how did you measure how much they were dragging before and after? Just jack the wheel up and spin it??

Yes, and no.

It started with me noticing the left rotor was hotter than the right. This lead to me rebuilding both calipers. Rotors were now even in temp but still a little warm and when jacked up, they didn't rotate freely.

Then I had the pleasure of working on my buddy's Metro and his were VERY free - and had no shims installed. The light bulb turned on.

All my life I've used the CRC brake squeal goop - it's dries rubbery. Little did I know that it was keeping the pads pre-loaded against the rotor.

Figure if the pistons only retract so far by design, you don't want anything compressible between the caliper and the pads if you want the pads to 'float' more.

As an added bonus, my brake pedal is firmer (maybe it's my imagination).

GM's low drag calipers
http://www.mpbrakes.com/uploads/documents/lowdrag.pdf

Mazda uses floating brake pads for low friction on the Mazda2. They simply adjust the lever arm of the brake pedal to make up for it.