As a hobbyist programmer, I've written several small utilities and screensavers:

Mac OS X Apps:

iConvert Icons

A simple utlity to convert ico to png, png to ico, and many other formats to ico, icns, and png.
 

Web 2.0 Apps:

iConvert

An online icon converter to convert ico to png, png to ico, and many other formats to ico, icns, and png.
 

Mac OS X Screensavers:

ClockBox

Just what the name implies; a virtual "box" of clocks that you can use to save your screen!
 

Linux / Open Source:

libicns & icns2png

A library for reading and writing Mac OS icons, with a tool for extracting PNGs from icns files.