This page has a few small programs I've written

Bash

[2010] mv_files_numbered
Moves files into a numbered order (00..99). It's a bit older and could use some cleaning up.
Usage is mv_files_numbered shared_beginning filetype all the files to be numbered
[2014-01] rename_using_lists
Renames a group of files. Useful when the names aren't changing in a pattern that's easy to give to the normal rename command.
[2014-01] rename_in_txt_files
Replaces strings in a whole group of text files.

The first is from an earlier time; the last two I created when I wanted to rename a bunch of interlinked HTML files.