I had a play with AviStack last night and was very impressed: http://www.avistack.de/index.html
For lunar images I think it does a much better job than Registax. It automatically does a very powerful multipoint stack which corrects for the "wavy" distortions caused by the seeing - I consider this essential for lunar images and it is something I've never had much success with in Registax - up to now I've been using IRIS to perform this correction.
AviStack does not do wavelet filtering - Registax is far more powerful for that. So you need to post-process your stacked image in Registax (at least until my new program comes along!)
There is a AviStack vs Registax comparative review here: http://joe.zawodny.com/index.php/2008/11/15/registax-vs-avi-stack/
Mark
That is a really interesting site by Joe Zawodny. I will study it in more detail.