I did some work towards the latest version of the Mac Blades of Avernum Editor, which now splits the view into several windows. You can get it from Niemand’s editor site.
I’ve also been working on porting some of the features of the Mac editor over to the Windows editor. I’m still working on it, and you can get the current version, Eccentric Eyebeast, HERE. The current plan is for the next release to at least look the same as the Mac version.