Indexo is the most smart, simple, light and small software with full features. It is a freeware file name changing application that's portable.
Here are some screenshots to illustrate the features and user interface of this application:
Modify file or folder names to add an index number or letter and other renaming rules. Screenshot of Indexo - 825px · 626pxPerks of a portable app. Screenshot of Indexo - 280px · 400px