What is it?
ATI Catalyst - cli.exe

What does cli.exe do?
cli.exe quote's are from the startup DB. There are 2 primary listings. One is called cli.exe systemtray and it is:
"System Tray access to ATI's CATALYST? CONTROL CENTER. Note that this has "SystemTray" appended to CLI.exe in the "Command" column of MSCONFIG. Not required to run the control center - which is available via a right-click on the desktop"

The second entry is called cli.exe runtime.
"ATI's CATALYST? CONTROL CENTER. Required if you want to change graphics settings on a regular basis but you must have internet access and Microsoft's .NET framework installed. Note that this has "runtime" appended to cli.exe in the "Command" column of MSCONFIG. If not you can start the program manually via Start -> Programs -> ATI Catalyst Control Center -> Advanced -> Restart Runtime "

Neither is needed by windows.