I have some important installed software applications, and I want to backup such applications only (not all disk). Is there any software that can backup those applications (including registry?)
No, not really. Windows does not store what registry keys a program uses so there is no real way for a 3rd party backup program to know what to save from the registry. The same goes for shared files like DLL's that may not be installed in your program's install directory.
One option is use a tool like sandboxie and install the program inside the sandbox. You then can look at the sandbox and see what files the program wrote out to. However this does not help you detect if the program needed a shared DLL, saw it existed, then did nothing. If you restore your "Backup" the DLL may not be there on the new system and the program may not work.