xlsh (2012)

Linux, C, PAM

This project aims to provide a convenient replacement for standard login program found on many POSIX compliant systems. It provides a basic login shell, similar to one found in GNU HURD, that apart from performing a login action, can also reboot or shutdown the system. It uses PAM for authorization and session management.

When desired using the xlshd daemon it can also sucesfully replace a display manager such as GDM.

Source code
Wiki