Over the years I've made many example files showing how to do many different things in game and application development in MMF2. Some show some experiments that MMF2 wasn't originally designed to do, but still possible with a little imagination. Other examples show how to make certain game types, visual effects or collision/physics behaviors.
Since 2003 I have written the occasional extension module as well which you can download from the 'Extensions' page.
Some of them are even open source so you can learn from them.