[NF] Tool for editing multiple files for huge search/replace operation

Literally about 10 years ago, I'm pretty sure this list suggested a tool that I used to update several text files in a common folder; it was a big "replace text 123 with 456" kind of thing. But alas, my memory is failing me and I can't recall what the tool was called.

Anybody know of such a tool to handle large search/replace across several text files in a same folder or even perhaps cascading tree of folders?

tia, --Mike