Calculate the volume of an object

Vitsy, 49 bytes

I thought you handed this one to me on a plate, but I found an unresolved bug to work around. Didn't hurt me, though.

lmN
3^43/*P*
2^*P*
**
v:++2/uV3\[V}-]V3\*12/^v*3/

Basically, with the input being a certain length for different functions, you spoon feed me my method syntax for doing this stuff. So, yay, success!

Explanation, one line at a time:

lmN
l   Get the length of the stack.
 m  Go to the line index specified by the top item of the stack (the length).
  N Output as a number.

3^43/*P*
3^
          Put to the power of 3.
  43/*    Multiply by 4/3.
      P*  Multiply by π

2^*P*
2^     Put to the second power.
  *    Multiply the top two items.
   P*  Multiply by π

**
**     Multiply the top three items of the stack.

v:++2/uV3\[V}-]V3\*12/^v*3/
v                            Save the top item as a temp variable.
 :                           Duplicate the stack.
  ++                         Sum the top three values.
    2/                       Divide by two.
      u                      Flatten the top stack to the second to top.
       V                     Capture the top item of the stack (semiperimeter) 
                             as a permanent variable.
        3\[   ]              Do the stuff in the brackets 3 times.
           V}-               Subtract the semiperimeter by each item.
               V             Push the global var again.
                3\*          Multiply the top 4 items.
                   12/^      Square root.
                       v*    Multiply by the temp var (the depth)
                         3/  Divide by three.

Input is accepted as command line arguments in the exact reverse as they appear in the question, with no trailing zeroes.

Try it online!

As an aside, here's something that's currently in development.

Java w/ Vitsy Package

Note that this package is work in progress; this is just to show how this will work in the future (documentation for this is not yet uploaded) and it is not golfed, and is a literal translation:

import com.VTC.vitsy;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Arrays;

public class Volume {
    public static void main(String[] args) {
        Vitsy vitsyObj = new Vitsy(false, true);
        vitsyObj.addMethod(new Vitsy.Method() {
            public void execute() {
                vitsyObj.pushStackLength();
                vitsyObj.callMethod();
                vitsyObj.outputTopAsNum();
            }
        });
        vitsyObj.addMethod(new Vitsy.Method() {
            public void execute() {
                vitsyObj.push(new BigDecimal(3));
                vitsyObj.powerTopTwo();
                vitsyObj.push(new BigDecimal(4));
                vitsyObj.push(new BigDecimal(3));
                vitsyObj.divideTopTwo();
                vitsyObj.multiplyTopTwo();
                vitsyObj.pushpi();
                vitsyObj.multiplyTopTwo();
            }
        });
        vitsyObj.addMethod(new Vitsy.Method() {
            public void execute() {
                vitsyObj.push(new BigDecimal(2));
                vitsyObj.powerTopTwo();
                vitsyObj.multiplyTopTwo();
                vitsyObj.pushpi();
                vitsyObj.multiplyTopTwo();
            }
        });
        vitsyObj.addMethod(new Vitsy.Method() {
            public void execute() {
                vitsyObj.multiplyTopTwo();
                vitsyObj.multiplyTopTwo();
            }
        });
        vitsyObj.addMethod(new Vitsy.Method() {
            public void execute() {
                vitsyObj.tempVar();
                vitsyObj.cloneStack();
                vitsyObj.addTopTwo();
                vitsyObj.addTopTwo();
                vitsyObj.push(new BigDecimal(2));
                vitsyObj.divideTopTwo();
                vitsyObj.flatten();
                vitsyObj.globalVar();
                vitsyObj.push(new BigDecimal(3));
                vitsyObj.repeat(new Vitsy.Block() {
                    public void execute() {
                        vitsyObj.globalVar();
                        vitsyObj.rotateRight();
                        vitsyObj.subtract();
                    }
                });
                vitsyObj.globalVar();
                vitsyObj.push(new BigDecimal(3));
                vitsyObj.repeat(new Vitsy.Block() {
                    public void execute() {
                        vitsyObj.multiplyTopTwo();
                    }
                });
                vitsyObj.push(new BigDecimal(1));
                vitsyObj.push(new BigDecimal(2));
                vitsyObj.divideTopTwo();
                vitsyObj.powerTopTwo();
                vitsyObj.tempVar();
                vitsyObj.multiplyTopTwo();
                vitsyObj.push(new BigDecimal(3));
                vitsyObj.divideTopTwo();
            }
        });
        vitsyObj.run(new ArrayList(Arrays.asList(args)));
    }
}

C, 100 97 bytes

#define z(a,b,c,d) d?d*sqrt(4*a*a*b*b-pow(a*a+b*b-c*c,2))/12:c?a*b*c:3.14159*(b?a*a*b:4/3.*a*a*a)

edit 1: remove unnecessary decimal ., thanks Immibis!

JavaScript ES6, _{129 126 125 116 114} 90 bytes

Saved lots of bytes (9) with a wonderful formula, thanks to Stewie Griffin! Since input must be nonzero, variable? will suffice for a defining-check.

with(Math){(a,b,c,h,Z=a*a)=>h?sqrt(4*Z*b*b-(D=Z+b*b-c*c)*D)/4:c?a*b*c:b?PI*Z*b:4/3*PI*Z*a}

Test it out!

with(Math){Q = (a,b,c,h,Z=a*a)=>h?sqrt(4*Z*b*b-(D=Z+b*b-c*c)*D)/4:c?a*b*c:b?PI*Z*b:4/3*PI*Z*a}
console.log = x => o.innerHTML += x + "<br>";

testCases = [[4], [5.5, 2.23], [3.5, 4, 5], [4, 13, 15, 3]];
redo = _ => (o.innerHTML = "", testCases.forEach(A => console.log(`<tr><td>[${A.join(", ")}]` + "</td><td> => </td><td>" + Q.apply(window, A) + "</td></tr>")));
redo();
b.onclick = _ => {testCases.push(i.value.split(",").map(Number)); redo();}

*{font-family:Consolas,monospace;}td{padding:0 10px;}

<input id=i><button id=b>Add testcase</button><hr><table id=o></table>