GUI batch renamer for Linux

Question

Need a batch renamer app for Linux.

I have 4 folders with 3 folders each. after the rename operation, I want to have

folder1
  - file1.txt
  - file2.txt
  - file3.txt
folder2
  - file1.txt
  - file2.txt
  - file3.txt
and so on.

When I try to use Krename => [$dirname]####, I get

folder1
  - file1.txt
  - file2.txt
  - file3.txt
folder2
  - file4.txt
  - file5.txt
  - file6.txt
and so on.

Any suggestion for a GUI app that can do it? Thanks