SearchMyFiles - Alternative to the standard Search For Files And Folders module of Windows. Duplicates search is also supported.
GNU M4 - GNU M4 is an implementation of the m4 macro preprocessor.
PowerGREP - Quickly search through large numbers of files on your PC or network using powerful text patterns to find exactly the information you want. Search and replace with plain text or regular expressions to maintain web sites, source code, reports, ...
XMLStarlet - XMLStarlet Command Line XML Toolkit
dnGREP - dnGrep allows you to search across files with easy-to-read results.
xmllint - command line XML tool