Scratch

If you are considering making a platform type game, check this out. It is a demo of nothing but a platform that moves up and down randomly, and a sprite that walks around and jumps while always landing in the right place without falling through the platform or the sides of the screen. Intentionally simple 

it is here...
http://scratch.mit.edu/projects/Locomule/1080017

and will be added to my collection of 'game routines' gallery here...
http://scratch.mit.edu/galleries/view/60830

...which also currently includes demos of...
Chase AI
Fake Depth
High Score Sorter
Asteroids type motion
Pong type bounce
ScrollX scrolling
ScrollX used to make a random dungeon
a scrollable race track
and a game where you play a fire-breathing dragon