WHM (WebHosting Manager) is the control panel for managing your server. It has tools to manage all features in the server such as server setup, reseller, account function, themes, etc.
cPanel is controlled by WHM. cPanel is a fully featured web-based control panel that allows you to manage your domain through a web interface. The idea is transfer as much of the control and responsibility of managing your web site to clients. Your clients can manage all aspects of e-mail, files, backup, FTP, CGI scripts, and web site statistics themselves. The default cPanel control panel is paper_lantern.
RVskin is the multi-languages, multi-themes advanced skin management software for cPanel server. Plus, it now provide WHM admin manager and single sign-on systems. More about RVskin.