ripgrep - ripgrep combines the usability of The Silver Searcher with the raw speed of grep.
dnGREP - dnGrep allows you to search across files with easy-to-read results.
ack - Ack is designed as a standalone (one perl file) replacement for 99% of the uses of grep.
AstroGrep - AstroGrep is A Microsoft Windows GUI File Searching (grep) utility.
The Silver Searcher - A code searching tool similar to ack, with a focus on speed.
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, ...