Lightweight, Cross-desktop Display Managerhttp://www.freedesktop.org/wiki/Software/LightDM
LightDM is a lightweight, cross-desktop display manager. Its main features are
a well-defined greeter API allowing multiple GUIs, support for all display
manager use cases, with plugins where appropriate, low code complexity, and
fast performance. Due to its cross-platform nature greeters can be written in
several toolkits such as Qt and GTK.