The first release, Simple Desktop Display Manager 0.1.0, was shared via Google+ to the world. As talked about in earlier articles on SDDM, it's a lightweight yet modern display manager that uses Qt and Qt Quick for making a very configurable display manager that is very lightweight and opens up lots of possibilites. The only har dependencies on SDDM are PAM, XCB, and Qt. In its months of development, it's been quick to get new features.
Right now SDDM is focusing upon X.Org Server support, but given its light dependencies and strong use of Qt, Wayland support will likely come to SDDM quite easily. SDDM has also taken the interest of the Hawaii Desktop Environment and there they already have their own Qt-based Wayland compositor.
The code to SDDM can be found on GitHub. Embedded below is the easily-developed "Maui" theme for SDDM.