The Lumina Desktop Environment is a lightweight system interface that is designed for use on any Unix-like operating system. It takes a plugin-based approach, allowing the entire interface to be assembled/arranged by each individual user as desired, with a system-wide default layout which was setup by the system administrator. This allows every system (or user session) to be designed to maximize the individual user's productivity. (View some examples)
The Lumina desktop developers understand that the point of a computer system is to run applications, so Lumina was designed to require as few system dependencies/requirements as possible. This allows it to be used to revitalize older systems or to allow the user to run applications that may need a higher percentage of the system resources than were previously available with other desktop environments.
All of this results in a very lightweight, customizable, and smooth desktop experience with minimal system overhead.
On the technical side of things, Lumina is created/distributed under the 3-clause BSD license, allowing it to be used by anyone, anywhere (including in proprietary distributions). It has been written from scratch in C++/Qt5 and is not based on any existing desktop's code-base. It also does not use any of the Linux-based desktop frameworks (ConsoleKit, PolicyKit, D-Bus, systemd, etc..), instead using a simple built-in interface layer for communicating directly with the operating system (which is the only class specific to the operating system - making it simple to port/customize). This allows it to obtain system information in a fast and efficient manner while ensuring desktop stability and reliability.
Additional Note for developers:
The Lumina desktop environment is not an application development toolkit/framework - it is only a system interface. If you want to create applications for users of the Lumina desktop, simply create/install the registration file(s) for your application according to the XDG/FreeDesktop standards (the desktop entry, menu, and autostart specifications in particular - depending on the needs of your application). If you wish to reduce the number of additional dependencies for your application on a Lumina system, simply write it using the Qt5 graphical toolkit and not the KDE-based variant/offshoot of Qt.