Rtorrent & Rutorrent install script needed.
Latest compatible versions and all needed software (Including rutorrent plugins)
The above script will need to have the ability for multiple users including ftp accounts (PROftpd preferred) jailed to their on download directories.
Also the ability to add or remove users at a later date this could be a separate script if needs be.
Http/s downloads would also be a good add-on.
Must be easy to use for users.
Choice of server OS will be up to you and which works best.
I have used other install scripts and they are either too hard for the user or if the server restarts their accounts no longer work. Also on a tight budget. :)