Free file Utilitaire, which allows to quickly rename group of files at once. It is very useful for renaming the group of files of similar types (pictures, databases, etc.).
You can select folder with files to rename. You can also specify file mask (for example: *.jpg;*.jpeg), which will filter selected files by the mask.
Rename*us allows to change extension of selected files at once.
You can specify file name schema for selected group of files. For example, if you specify 0001 schema, selected files will be renamed as 0001, 0002, ..., 0010 and so on.