Java Applets from "Physics by Computer":

Driven pendulum	(source code)
Ising Ferromagnet	(source code)
Quantum particle in a box	(source code)
Percolation I (Growth Algorithm)	(source code)
Percolation II (Hoshen-Kopelman Algorithm)	(source code)
Hofstadter Butterfly	(source code)
Frenkel-Kontorova model: Particles in a periodic potential	(source code)
Diffusion Limited Aggregation (DLA)	(source code)

Applets from "Programmierkurs für Naturwissenschaftler und Ingenieure":

Bose-Einstein condensation	(source code)
Learning random patterns by a neural network (perceptron)	(source code)
Time series prediction by a neural network (perceptron)	(source code)
Avalanches of a model of selforganized criticality	(source code)
DISX - the game of avalanches	(source code)
Bak-Sneppen model of selforganized criticality	(source code)
Julia set of the quadratic map in the complex plane	(source code)
Mathematical ant which follows its own trace according to simple rules	(source code)
Pictures of the denominator of all rational numbers between zero and one.	(source code)
Selforganized Criticality	(source code)
Travelling Salesman Problem