AE3D has recently released the DarkCorner GPU-based Ambient Occlusion plug-in for Adobe After Effects for Mac OSX. DarkCorner quickly and interactively computes Ambient Occlusion for a given image or an image sequence and depth (Z) information, using the power of your GPU. The depth channel can be supplied within image formats like .rla or .rpf, or as a separate image sequence.

From the AE3D Post: Due to overwhelming demand from our users, we have ported our SSAO plug-in DarkCorner and the Antialiasing plug-in JaggyBuster to Mac OSX. Both plug-ins are now available for OSX Lion (with OpenGL 3.2 support) and work with After Effects CS5 onwards. For more information please check darkcorner page.