LightDM is described as 'cross-desktop display manager. A display manager is a daemon that:' and is an app in the OS & Utilities category. There are three alternatives to LightDM for Linux, Xfce and BSD. The best alternative is Ly, which is both free and Open Source. Other great apps like LightDM are SLiM (Free, Open Source) and XDM (Free, Open Source).