The Full Screen Editor is a Spectrum utility which can be used to edit
text or BASIC programs.  It is based on a mainframe editor and is easy
to use and quite powerful.  It is compatible with +3 disk and with the
microdrive.

Full instructions and a binary are contained within the zip file.  The
binary consists of just the editor code.  This can be loaded into the
"xzx" Spectrum emulator, for example, by defining LOAD_SAVE_2 and using
the BASIC instruction LOAD "fse" CODE nnnnn.