Apps with 'Regex substitution' feature

Vim ("Vi IMproved") is an advanced text editor that allows syntax highlighting, word completion and has a huge amount of contributed content. It also has a GUI version called GVim.

A simple programmer's editor with a tightly-integrated console.

Multi String Replacer is a small and portable application that can be used to replace multiple strings at once. Its main functionality is String Swapping in which can be easily and quickly done. String swapping consists on replacing WordX with WordY and WordY with WordX.

sed (stream editor) is a Unix utility that parses text and implements a programming language which can apply transformations to such text.