It creates a single distribution executable for your program that can handle things like creating icons and folders in the user's Start Menu, installation and deinstallation of DLLs, ActiveX controls, fonts, screen savers, etc. It claims that it only adds 60Kb to your program, which compares very favourably to many other installers. After registration, you'll get a one-year licence for the installer. It can also install an uninstaller for your application files. The program also supports disk-spanning, useful for all of you who have applications that span many floppy disks.
Development is ongoing, and there is support for other languages.
My personal favourite . It is able to self-register ActiveX and COM controls. It looks like it does not use any script files nor does it support the command line interface - you must use the supplied GUI configuration program. I have little information about this setup utility, other than that it is free. Check it out yourself and let me know if you have more information.