c99shell from the ccteam was a great PHP script, unfortunately support is discontinued. The idea is to have an all-in-one file to administrate a server once that file is uploaded.
When you look into the source of the c99shell it is a bit chaotic and it even is detected by some anti-virus programs. For these reasons I wrote the code of QedShell from scratch.
This project is also aimed the help learn PHP, for that reason I commented almost evory line.