So far, the vast majority of 'for fun' coding I've done has been in the Python scripting language. I first got started on it when I was working at NPL, where along with its Win32 extensions it allowed to me to automate document creation in Microsoft Word relatively painlessly.
While I was learning how to use Python, I made a number of 'toy' scripts - ones that performed small tasks, usually to automate repetitive jobs - such as batch file renaming, which I found to be inordinately difficult to do in Windows. In some cases, the purpose of a program was merely to do extremely basic, though tedious, mathematical calculation (for example, if I walk x metres on a world of circumference y metres, then how much further has my head travelled than my feet, given that I am 178 cm tall?).
The listings linked to here provide a few examples as plain text. Feel free to use, extend or modify them as you wish - if you think I might be interested in the resulting creation then give me a shout.
This script generates a file in the current working directory containing the compton scatter distribution at energy arg at filename arg.
This script outputs your computer's (local) IP address and host name.
This script is a basic metronome.
This script provides reference pitches for tuning.