File Substring Replacement Utility (FSRU) performs search and replace operations with multiple strings in multiple files. It was designed specifically for computer programmers working on large projects with many source code files, however any type of file can be used, including HTML. Search and replace operations can also be performed on filenames (mass renaming). A detailed log is kept of every substring that is found and replaced. Case-insensitive, "whole word", command line, and wildcard searches are supported.

Version 8.0 adds "Common Tasks" toolbar, "Swap search/replace strings" tool, support for null characters.