MarcEdit is a freeware tool with the capability to integrate with Koha directly. Once a connection is established, users can pull records from Koha, make changes with the wide variety of tools available in MarcEdit, then push the changes back into Koha.
MarcEdit is also a great tool for processing records prior to import. For example, vendor records can be opened and modified in batch to align to local standards, remove unnecessary information, and even generate items with relative ease.
MarcEdit is developed by Terry Reese.
Project Link: https://marcedit.reeset.net/