Xgl was attempt to do the same thing by SuSE, which led to lot of opposition from other Linux distributors. This spawned competing AIGLX project (mostly associa

Xgl was attempt to do the same thing by SuSE, which led to lot of opposition from other Linux distributors. This spawned competing AIGLX project (mostly associated with RedHat in that times), which solved the same "problem" from the other end and enabled such graphical effects mostly as an side effect and in contrast to Xgl without degrading performance of OpenGL applications (Xgl did not allow it's clients to use hardware acceleration). The difference is that both Looking Glass and Xgl works as an proxy X server. While AIGLX was an effort to make client-side libgl implementations usable from the X server itself, which is good for Acceleration of GLX in Indirect mode (hence AIGLX) but also as a general HW acceleration backend for things like XRender and XVideo (for example intel driver emulates XVideo in terms of OpenGL) and with addition of one simple OpenGL extension (ability to create GL texture from contents of X11 window/pixmap) allows all the 3D window manager tricks.