The Blaschke Boundary Interpolator is a Java applet for solving the following interpolation problem:
Blaschke boundary interpolation: Given N distinct points on the unit circle. Find a Blaschke product of degree N that identifies these points.
The algorithm implemented here is described in my article Constructing interpolating Blaschke products with given preimages.
To use the applet, first choose the interpolation points, and click 'Initialize'. Then use the 'Iterate' button to step through the algorithm. You can also move the zeros manually.