Enlightenment is an extremely configurable window manager that has gained quite the reputation over the years. It is notable for being able to display some visually impressive themes that are difficult to reproduce on other window managers.
The current 0.16 release aims to act, in a sense, as a "conventional" window manager. Since this release, work has begun on the EFL (Enlightenment Foundation Libraries). The aim of these libraries is to create a set of GUI programming tools similar to those of Qt and GTK. However, the EFL aims far beyond the limits of other tools and includes innovative and unique approaches to developing modern desktop apps.
Current push for the 0.17 release is to have Enlightenment move beyond the realms of just providing window management services but to also provide desktop shell capability including integrated file management tools.