HANANH  You mean OmniDiskSweeper by OmniGroup - yeah the ninjas at Omni have made some of their older great software freeware lately - appreciate that step!

But ID-Design has done the contrary way with WhatSize:

The former freeware is now shareware (nagware).

Although there are free alternatives yes true, but this does not mean there is no demand -

If it's a well designed and continuously supported app (made sure it's compatible with the latest Mac OS versions) with additional features it will be great.  
(Version 1.0.1)