John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types commonly found on Unix systems, as well as Windows LM hashes. On top of this, lots of other hashes and ciphers are added in the community-enhanced version (-jumbo), and some are added in John the Ripper Pro.
rpl is a Unix text replacement utility. It will replace strings with new strings in multiple text files. It can scan directories recursively and replace strings in all files found. The search can be limited to files with certain filename suffixes (e.g. '.html', '.c', etc.). It includes source, a build script, and a man page. It should work on most flavors of Unix. Linux/Intel, Linux/PPC, and source RPMs are available, as are binaries for other OSes, including Mac OS X.
Change is a non-interactive text editor, similar to sed, but much easier to use. It works by substituting a specified target pattern in the source text with another specified text pattern. It can operate on multiple files specified on the command line, or it can operate upon stdin/stdout in filter mode.