gl is an X server that uses OpenGL for its drawing operations. Together with a compositing window manager such as Compiz or newer versions of Metacity, it allows for excellent quality 3D and 2D desktop effects
AIGLX is a project that aims to enable GL-accelerated effects on a standard desktop. We have a lightly modified X server (that includes a couple of extensions), an updated Mesa package that adds some new protocol support and a compositing window manager.
Beryl has had many names, but is basically a fork of Compiz with additional features and plugins. Beryl used to be Compiz-Quinnstorm. Beryl does not depend on gconf and gtk like its Compiz counterpart does.