grep - grep is a command-line utility for searching plain-text data sets for lines matching a regular...

mlocate - Indexes filesystems allowing you to search for files.

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, ...

Everything by Voidtools - Everything. Locate files and folders by name instantly. Everything. Small installation file. Clean and simple user interface.

dnGREP - dnGrep allows you to search across files with easy-to-read results.

DocFetcher - DocFetcher is a portable German/English open source desktop search application.