The Geoanalytics Image Pyramid, ga_pyramid has had an initial release on GitHub today.  With this release, you can store tiled image pyramids, like the kind used to store the satellite imagery of Google Earth.  Features of ga_pyramid that you may not find in other packages:

• Supports 16 and 32 bit images, including floating-point images.
• Supports adding time and elevation dimensions to the pyramid.
• Supports very-large pyramids via sharded MongoDB collections.

Future releases will concentrate on flexibility and performance, but this initial cut seems useful enough to announce as a release.  Find it on GitHub