An editor program allows the user to create and modify simple text files. This is as opposed to a word processor program which usually allows formatting, fonts, italics, and other stylistic devices intended to look better when printed out - an editor is simply designed to edit text. Because of this, editors are often used to write computer programs, configuration files, web pages, and other technical files that are read by other computer programs, not only by people.
Please mention which operating system or systems the program runs on. The exact price doesn''t matter, since these things change often, but do say if the program is open source, free, or shareware.
A hex editor is a program intended for editing binary files, usually executable program files, one byte at a time. This is useful for machine language programming and debugging at the lowest level. Most, but not all, powerful text editors can also edit binary files, and vice versa.

SED

SED (Stream EDitor) is a non-interactive editor, written by Lee E. McMahon in 1973 or 1974 for the Unix operating system, but now available for most OS's. Instead of the user moving the cursor on the screen, the user sends the program a script of editing instructions. In this sense, SED works like a filter - deleting, inserting and changing characters, words, and lines of text. This makes it particularly useful in batch files. Its range of activity goes from small, simple changes to very complex ones.
Minimalistic cross-platform text editor by Jon Skinner.

Vi

Love it or hate it, vi is the text editor many grow to love. Vi is powerful, configurable and widely available - not just for Unix, clones exist for many platforms.