you could try vi. It's on every system. It can be a bit tedious to use at first, but if you get it 'in your fingers' it's really a very useful editor.
Very very very short tutorial:
open a file
vi <filename> (if it doesn't exist, it's created now) <enter>
scroll through the file with either the arrow keys or with the h-j-k-l keys (left-down-up-right).
To insert text, type i (INSERT appears on the bottom line)
To delete text (one char at a time), you can use DEL on most systems, either in INSERT mode or noet inINSERT mode ... to stop editing, press ESC.
To save the file type (not in INSERT mode!)
:wq! (the : gives you a command prompt on the bottom line)
To exit without changing the file enter
To view a file you can use LESS.
Scroll through the text with arrow keys or PGUP/PGDWN keys.
Hope this helps.
There is also a more extensive builtin tutorial in vi. It takes about 30 min to complete and teaches you some more tricks (like search/replace and the like). You can enter this tutor in the help file:
in the help file, scroll down until you find the tutor tag [tutor];
place your cursor on it and press ctrl-]