ubuntu MATE 15.04 Beta2 PowerPC kernel 4.0 with the Xorg and Mesa downgrade installation.Download: Xorg_and_unofficial_Mesa_for_ubuntu_MATE_15.04_AMIGA_one_X1000.tar.gz
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I tested Compiz with ubuntu MATE 15.04 PowerPC today. Compiz is an OpenGL composite and window manager. You can activate it with MATE Tweak. Compiz works very well with the unofficial Mesa.
Another screenshot of the Compiz cube on ubuntu MATE 15.04 PPC: