the_silver_searcher - Interesting for anyone who, like me, manages and searches through large source trees. Essentially something like ack - an automatic grep that runs through entire hierarchies and additionally filters files by various patterns, taking into account gitignore and hgignore. And all this not as a Perl script like ack, but in C with various native libraries and various optimizations for searching. It doesn't get faster than this unless you use pre-generated indexes (which come with their own problems).