Droplets is a GDM theme made from a pretty wallpaper.
GDM (the GNOME Display Manager), a graphical login program, provides an alternative display manager for the X Window System.
The X Window System by default uses the XDM display manager. However, resolving XDM configuration issues typically involves editing a configuration file. GDM allows users to customize or troubleshoot settings without having to resort to a command line. Users can pick their session type on a per-login basis. GDM also features easy customisation with themes.