OSPEdit is a (really) simple on-site source code editor, written in PHP
/!\ Warning, ospedit can browse for folders, wipe files and give access to your web site source code to anyone if misused (or not); use it at your own risk !!!
Just change the default password ("###_YOUR_PASSWORD_HERE_###") and eventually the inclusion path of jQuery/jQuery ui/Ace/spin.js/toastr js and css scripts.
Note : excepted jQuery and jQuery ui, theses third-party library are not mandatory, you can disable any of this third-party library by deleting scripts/link tags
OSPEdit can use the excellent Ace editor to use syntax checking/highlighting.