Forum .LRN Q&A: Response to Has someone done a comparision of dotLRN with other commercial systems?
Now I am going to try to address your original question: we are in the process of completing a comparison of various commercial and non-commercial systems. Our experience has shown that this is not a very easy process, because the results become stale very quickly and it is very hard to do much more than superficial testing on most systems.
More interesting are the criteria that one uses to make the choice as well as the quality of the implementation of the various functions from the user's perspective (as Michael mentions above... which we have learned the hard way). I will try to sort out some of the criteria we are using right now and will post them here for discussion as soon as I can. Obviously each entity considering dotLRN will place a different emphasis on the various criteria, which is why providing a framework to help decide is probably more useful than an actual comparison (which is useless in a couple of months anyway, due to the constant flux in the marketplace).
The fact that most of the documentation on dotLRN has not appeared yet makes it hard for someone that does not know the history behind dotLRN to make an informed choice. Here is the document that originally woke my interest in ACES many moons ago: http://web.archive.org/web/20010405233725/www.arsdigita.com/doc/overviews/education.html
I know it is very old and not all of the original ideas have been implemented, yet it does provide a good starting point to read about the original goals behind dotLRN. This is the kind of documentation that is missing right now for dotLRN (this is not just a problem that exists in the dotLRN sphere but on the OpenaACS site as a whole... we need something like the old asj). This kind of documentaion is critical for the future of the platform. Having clearly defined goals will help prevent dotLRN drift (which I feel is a major problem with a lot of opensource projects).
The major strengths of dotLRN seem to lie in the philosophy and people behind it, its modularity, easy extendibility, its proven solid architectural foundation, all the packages that are just waiting to get ported from ACS and OpenACS, and if something is not working the way it should you can have it fixed or fix it yourself. As soon as MIT, Openforce, and Berklee pull this off others will be able to take the stick and keep on running (while they continue to work as well), building on top of it without having to worry to much about scalability. The money that is saved on licensing can be put into development. It seems that Blackboard and WebCT both now realize the development potential their customers have and have reacted by creating sandboxes for their customers to play (Blackboard Buildingblocks and WebCT Vista's Software Development Kit).