V-Grep

V-Grep is a simple, easy to use, but effective, software which provides basic expressions power to the typical Windows users.
Even in DOS you could use masks, to speed-up searching for files. These masks were later adopted for use in Windows. Masks are special types of strings that with the help of reserved characters - here it would be an asterik and question mark - allow you to easily describe complex patterns.
Regular expressions are using basic concept of the masks but they add even more special characters that can represent definite number of characters, optional phrases etc.
Users can specify expressions representing complex patterns that are difficult or impossible to find using only masks, such as: e-mail addresses, telephone numbers, IP addresses etc. In the Unix-class systems regular expressions are handled by a program called GREP (Global Regular Expression Print).
V-Grep (Visual GREP) gives you whole functionality of GREP and lots of other very useful options - all packed in a typical Windows GUI. V-Grep allows you also to search for files even without any knowledge about regular expression, but even then its much better way to do this than by using Windows built-in search feature, mainly because of a more legible search results.