A good way to clean rusty tools is by using some lemon juice with enough salt added to the paste. Dab the mixture on the rusted area and then rub gently using a dry cloth. Another good way is by using a sand paper to gently scratch the outer rust away. Using naval jelly or WD-40 is also another good way to remove rust.
First, are we talking wrenches and ratchets, or shovels and rakes, or bigger?
For small tools, the best penetrating lubricant I know of is PB blaster, as commented above.
For larger surfaces, I suggest using a simple wire brush to remove the loose rust, prior to applying any chemicals. Choose the appropriate coarseness of the brush for the tool and amount of rust. Then, I would use naval jelly. It's probably the best thing out there for rust removal, but it is a little nasty. It is a gel form of Phosphoric Acid. It has the added benefit of converting a certain form of rust into black ferric phosphate. The coating can then be left in place, to provide moderate further corrosion resistance, or it can be scrubbed off, leaving a fresh metal surface.
WD-40 is only good for fixing squeaky door hinges, and the ingredient in Coke that makes it do anything is Phosphoric acid, and it will only remove a small amount of surface rust.
I will admit, I haven't tried the lemon juice/salt or lemon juice/vinegar combinations suggested above, but I can say that lemon juice contains a high amount of citric acid, vinegar is diluted acetic acid, so if they work, that is why...