If you are not a scientist or into analyzing data, you probably won't be interested in most of these programs. In particular, the IDL, Matlab, and Labview programs are useless unless you have the software to run them (if you do use them, see this page on the difference between Matlab and IDL.
If you're not into data analysis or hardware, then you still might find some of these things useful. For windows users, VBScripts can be a huge help in automating common user tasks such as opening a series of programs or folders, mapping a network drive, or checking on the status of filesystems across a network. For Mac users, the Applescripts can do the same sort of things. One of the places where one might find them to be useful is with organizing music in iTunes. There is a program called Hyphen_Separator.scpt that will go through a set of highlighted songs in iTunes and check to see if they are in Artist-Songname format. If they are, it will attempt to fix the ID3 tag so that they are organized properly in your playlists.
Perl and Python are a great help if you do work with text and have issues where you need to cut and paste or delete alot of text throughout various files. They are very user friendly and the documentation for both is great. These languages also provide interfaces to MySQL functions so that you can create and access information from databases. Also, combined with CGI (Common Gateway Interface), perl allows you to do alot of stuff for free that would cost lots of money if you used commerical software.
I've provided links to examples that I've written or stolen from others (I try to give credit in the comments) and documentation for people who might want to use any of these languages to make life a little easier.
Lastly, I put together some instructions on ways to get all your iphone text messages onto your computer for free and delete duplicate songs in iTunes. Most people won't have the the patience for the latter, but if you're like me then you'd rather spend a whole afternoon trying to do these things than paying for a 3rd party program that does it.