LightDM

LightDM is a cross-desktop display manager. A display manager is a daemon that:

Runs display servers (e.g. X) where necessary. Runs greeters to allow users to pick which user account and session type to use. Allows greeters to perform authentication using PAM. Runs session processes once authentication is complete. Provides remote graphical login options.

Key features of LightDM are:

Cross-desktop - supports different desktop technologies. Supports different display technologies (X, Mir, Wayland ...). Lightweight - low memory usage and fast performance. Guest sessions. Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable). Comprehensive test suite.

The package name is generally "lightdm".