These are products that used to be useful, but may not work with newer operating systems, and other sites have more capable alternatives.

Windows Software

m3uEdit icon Download More Info m3uEdit 1.2
A simple m3u playlist editor. Drag-n-drop media files into the order you want. Freeware for personal use.
  Download More Info PicPop
Shows a picture's thumbnail in its context menu. Click on it to open it in a window. Freeware for personal use.
Try XnView's shell extensions instead.
  Download More Info EnvMath
A small DOS program enabling math operations at the command line and in batch files. You can use it to count how many times a program is run, control batch file looping, create parameters on the fly for other programs (including Windows programs!)...
Note: Does not work on NT systems (including Windows 2000, XP, etc.). $10.

Macintosh OSX Software

Thumbnail Browser icon Download More Info Thumbnail Browser
Point Thumbnail Browser to a folder and see a thumbnail of each picture. Click them to see the picture in a window or fullscreen.
Originally more of an experiment but turned out useful. There are better products out there. Freeware for personal use.

“...Yeah, even in the slowness, a big program can be full of surprises.”
Pham Nuwen, A Fire Upon the Deep, Vernor Vinge