The February issue of Sky and Telescope has a rave review of Avistack. Apparently, everything in the article is true. It does exceptionally well with the moon. 233 frames of 465 stacked, lots and lots of graphs, a light show while processing. This image had 2095 reference points displayed as polygons that mosaic-ed the image. Each frame contributed only the sharpest polygons to the stack. No frame was perfectly sharp. I tried to stop sharpening when the crater chains were revealed, and you can also see the terraced walls of the larger craters. The penalty is processing time. This took two and a half hours start to finish, but it is my first time, and the computer fell asleep partway through.
The claim is it runs on a mac. True, if you like X11 in a VM. It really works in Windows 7.
Below, Registax 5