Metamorphose

Renames files and folders at the same time.
Preview every item to be renamed before comiting changes.
Load all files in directory and in subdirectories (recursive renaming).
Undo renaming operation in case of mistakes.
Rename MP3 files according to their ID3 tags.
Full unicode support means any character from any language can be used.
Use of all allowed characters under Windows and OSX, all except ':' in Linux.
Save all program settings to file for later use!
Renaming operations:
Prefix
Suffix
Set file extension.
Replacement, modification, or move by: Character, position, or regular expression.
Insertion by: Position or every (number) characters.
Length modifications (padding, truncating, or both).
Renaming styles: combination of: user text, numbering, id3 tags, date, time.
Modifications: UPPERCASE, lowercase, Capitalize first, Title Style, sWAP cASE, 'DoRkIfY'
Move by position, text, or regular expression.
Sequential numbering (enumerating) options:
Use integers, alphabetical, or roman numerals
Pad with any valid character to any width.(integers only)
Control step size, starting number, reset count.
Set date and time manually or get from system.
Use supplied defaults or specify your own date and time formats.
Modular design allows great flexability and control, while keeping the easy stuff simple.
Python and open source (GNU-GPL) means it's quickly, easily, and legally customizeable to fit your needs. Read the License for more details.
Easily translatable with GNU GETTEXT utilities.