Multimatrix are matrix routines to make life in OpenSCAD easier. It allows you to multiply the geometry of all child elements with the given 4x4 transformation matrix.
//translates the cylinder  by [10, 20, 30]
multmatrix(m = [ [1, 0, 0, 10],
                 [0, 1, 0, 20],
                 [0, 0, 1, 30],
                 [0, 0, 0,  1]
               ]) cylinder();
//rotates by 45 degrees in XY plane and translates by [10,20,30]):
angle=45;
multmatrix(m = [ [cos(angle), -sin(angle), 0, 10],
                [sin(angle), cos(angle), 0, 20],
                [0, 0, 1, 30],
                [0, 0, 0,  1]
              ]) union() {
   cylinder(r=10.0,h=10,center=false);
   cube(size=[10,10,10],center=false);
}