(Search-n-replace done right)

... conditionally swaps one string with another ... EVERYWHERE ..., using a host of options, such as whole-word search, comment-/string-exclusion, interactive verification, and more, to ensure you don't shoot yourself in the foot. It can even produce a mass-verification preview for you to be certain that the changes are just/only what you really intended before committing them.

(Used heavily by Sweeney and Optimus.)