SLiM is described as 'Lightweight and elegant graphical login solution' and is an app in the OS & Utilities category. There are eight alternatives to SLiM for Linux and BSD. The best alternative is Ly, which is both free and Open Source. Other great apps like SLiM are SDDM (Free, Open Source), emptty (Free, Open Source), LightDM (Free, Open Source) and XDM (Free, Open Source).
XDM (in full, the X Display Manager) is the default display manager for the X Window System. It is a bare-bones X display manager. It was introduced with X11 Release 3 in October 1988, to support the standalone X terminals that were just coming onto the market.