This shader is an ambient occlusion for maya software render.
It was released maya 2008, 2009, 2010, 2011, 2012 and 2013 for Windows 32bit and Windows 64bit.

Installation

• Put "plug-ins/[maya version]/yiAmbientOcclusion.mll" and "plug-ins/[maya version]/key.lic" into plug-ins folder.
• Put "icons/render_*.xpm" and "icons/render_*.png" into pref/icons folder.
• Put "scripts/AE*.mel" into scripts folder.
• Load the "yiAmbientOcclusion.mll" from plug-ins manager.
• You'll find the "yiAODiffuseShader", "yiAmbientOcclusionSader" under Surface, and you can also find the "yiAmbientOcclusion" under General Utilities.

How to use

• Assign this shader.
• Turn on Raytracing in Render Setting.
• Set 1 or more Reflections in Raytracing Quality when useing "add transparency".

• Color : Base color.
• Transparency : Transparency color.
• Samples : Number of sample ray. The ray is shot it becomes a square of the sampling value. (3 means 9 rays)
• Distance : Calculated distance. It becomes infinite when set to 0.
• Spread : Calculated spread.
• Receive Transparency : When turned on, the transparency is calculated. keep in mind, this mode might take some time.
• Falloff : Modulus of decay.

• yiAODiffuseShader : It's an ambient occlusion plus diffuse.
• yiAmbientOcclusionShader : It's a basic ambient occlusion shader.
• yiAmbientOcclusion : It's a utility. It can be connected to other attributes.

Version History

• 1.0.1 : added maya 2010 32bit version
• 1.0.2 : added maya 2011 32bit and maya 2011 64bit version
• 1.0.3 : added maya 2008 32bit and maya 2008 64bit version
• 1.0.4 : "Add Transparency" label change to  "Receive Transparency"
• 1.0.5 : added maya 2012 32bit and maya 2012 64bit version
• 1.0.6 : added maya 2013 32bit and maya 2013 64bit version

More details are here.
http://yikuta.blogspot.com/2009/11/ambient-occlusion-for-maya-software.html

Let me konw if you have any problems.
Enjoy!