A thread recently discussed a program AVIStack v Registax. Sometime I downloaded it and couldn't figure it out but tried it out over the last couple of days reading the manual and got someinteresting results.
Watching how it works it the most surprising and now a convert to is capability and after reading the manual ease of use.
Interface doesn't look glorious but the age old expression looks can be deceiving.
1st image is Registax
2nd image is AVI Stack
3rd AVIStack
There maybe not much difference between the 1st and 2nd but registax image if you look carefully show line where it was difficult to align the images to stack. Whereas AVIStack stacks a lot more evenly.