LightDM

LightDM is a cross-desktop display manager whose aim is to be the standard display manager for the X.org X server. The key features ( as listed by upstream ) are:
 * A well-defined greeter API allowing multiple GUIs
 * Support for all display manager use cases, with plugins where appropriate
 * Low code complexity
 * Fast performance
 * No dependencies on Gnome libraries

Installation
LightDM is available on Gentoo Linux and supports the following USE flags:

Starting from version 1.1.3, LightDM does not build any greeter, so you need to build them separately. The following greeters are available.

The following use flags are available for the GTK+ greeter.

You can install lightdm using the following command:

Install the appropriate greeter using one of the following commands:

Configuration
The configuration file for LightDM itself is:

KDE
The LightDM KDE greeter also provides a KCM (KDE Control Module), which appears in the System Settings under System Administration → Login Screen (LightDM)

RazorQt


To have lightdm start at boot set the DISPLAYMANAGER variable in to lightdm, as shown below:

Finally, add xdm to default runlevel: