How to getting started with Object Oriented programming and runtime polymorphism? Here are two examples written in Component Pascal.
OO Shape Example.
Shapes provides an abstract interface for supporting graphical IO methods. You found examples written in other languages at Chris Rathman's website http://www.angelfire.com/tx4/cus/shapes/. Also have a look at Jim Weirich's page http://onestepback.org/articles/poly/ for this topic.
OO Collection Example.
Collections shows how to write data to files and read them back from files. Attila Truszek ported the implementation of Collections from Borland Pascal 7.0 to Oberon/F and I translated them from Oberon/F to Component Pascal (BlackBox 1.5).