AIGLX is 'Accelerated Indirect GL X'.
There are three interesting pieces of technology here:
1.
An updated Mesa that includes accelerated indirect rendering. This allows the compositing manager to do GL operations through the server instead of having to push window pixmaps from the COMPOSITE extension down to the client and then back up to the card.
2.
A version of metacity with a compositing manager enabled. It has a few effects implemented, including window minimzation and drop shadows.
3.
An updated X server. This X server is a devlopement version of Xorg that contains support for a new extension to improve performance. It can be installed along side your usual X server.