Enlightement with the default "Bluesteel" theme. The top four windows along the right edge are workspaces. The bottom window on the left is the icon manager. Right in the middle is the main menu.
Enlightement with one of the four supplied themes, this one titled "Ganymede." Notice that it put the titlebar on the Gimp sideways, presumably because there was more space in that direction. When the screenshot was taken, the pointer was over the Gimp image in the workspace window for the current workspace so you see the floating help indicating the application name.
I tried both 0.16.5 (dated October 2000) and 0.16.6pre (dated September 2003).
Documentation shipped with the RPM is poor. Online docs may be better.
It's Enlightenment. Nothing has better theme support than Enlightenment.
Enlightenment was the child of "Rasterman" and "Mandrake." Rasterman is still working on the project, but I'm not sure of Mandrake's involvement any more. Enlightenment started out as an ambitious product and has, if anything, become even more ambitious with time - without ever reaching a reassuring version number. Their intention in building Enlightenment was to create the best looking and most flexible window manager in existence so that the user could make it look and feel exactly as they want it to. Enlightenment is eye-candy central with very flexible behaviour, but with that comes size. And their ambitions (in my opinion) have far exceeded their grasp: the last "stable" release prior to September 2003 was 0.16.5 in October 2000. Development continued, but mostly on version 2 which is supposed to be a "desktop environment" rather than a window manager. I don't think v2 has made it out of CVS yet. In September 2003 version 0.16.6pre was released, perhaps in recognition of the fact that v2 was still a ways away.
I've used version 0.16.5 in the past, but didn't like it because of its size, and something about its behaviour has always bothered me - as much as they try to make it flexible, they still have to make certain assumptions about what it should do. I can't really explain this. I recently used 0.16.6pre and had major problems with the workspace support: only the first workspace functioned properly. I've had no such problems with 0.16.5 and would recommend you use that if you want to try Enlightenment.
One thing that Enlightenment does well is configuration. Everything is done through the extensive menu system, and look and feel can be configured to your liking. Settings are remembered between sessions. The workspaces are shown in small windows that are screenshots of the workspaces, and windows can be towed from workspace to workspace there.
Extremely flexible appearance and behaviour.
Big. Too complex.
Development continues on the new version, but it would appear that community interest is fading as the promised 2.0 release remains vapour.