Power users will love GrepWin, a free search-and-replace tool that enables regular expression searches from context menus in Explorer. It essentially adds a sophisticated interface to the grep command-line search tool developed for Unix and used in Linux, MacOS, and other operating systems, including Windows. It can replace whole strings of text in compatible files and documents, such as text files. Regular expressions (regex) enable incredibly specific searches, such as words with a specific number of letters or sequence of vowels, or "cats" when preceded by "house" or "wild." With special characters, groupings, and syntax, it's a science unto itself.