This project was implemented as a Ruby Summer of Code project, and the guys have some of the best mentors around. It just works, and it works well. It's extremely new and I think the source could do with some work, but the interface is beautiful and it's extremely simple to use. These guys have done well and I can honestly see this library being a huge part of Rails application administration
Not really, other than it's a port of MerbAdmin, which actually uses the Django stylesheets and Javascript (to the point where it violates the license, by failing to reproduce the text of the BSD license).
Thank you for pointing this out. Before I started the project, I requested permission from Wilson Miner to use the stylesheets and javascripts from Django and added his name to the acknowledgments, but I neglected to add the BSD license.
I looked through the code quickly, and it seems to rely on ActiveRecord for the History model.
However it probably wouldn't be too difficult to make an ORM-independent version of this, if that's the only place ActiveRecord is used. An admin tool really only needs to use the models that you have created elsewhere in your project. So they could make the history part of this configurable and allow you to supply your own model to handle those functions. It would be like how most authentication modules let you write your own User model, as long as you put a 'magic include' in that model to pull in the authentication stuff.
It very simple to write a quick DataMapper adapter for RailsAdmin. The thing with the history model is going to be changed probably on Saturday's BugMash.