Hello Niall,
I think the main tool would be image registration that is not too specific to stars, and this might really be two tools: one to find matching features in a set of images and another to remap the images so that the overlapping features are aligned.
DynamicAlignment goes down this path, but it is largely manual and only works with a pair of images at a time.
As a comparison, with Hugin or PanoTools, an arbitrary number of images can be provided and there are a few algorithms to choose from that will generate matching feature points automatically (of course there can/will be manual point manipulation too). It would also handle geometric and photometric distortions to ensure the images align properly. Finally, it blends images spatially and by exposure.
My thought process is: since combining multiple images is normally a very important part of the astrophotography process, it might make sense to have alternative aligning solutions for slightly different tasks. Juan discussed some important pros/cons about what already exists in the thread I linked.
As far as specific tools go, the Hugin/PanoTools packages contain numerous tools to facilitate pano and HDR merging, but I think the important ones that are lacking here are:
http://wiki.panotools.org/Cpfind = detects interesting features in images
http://wiki.panotools.org/Nona = handles remapping including distortions
