The Wikipedia editing tool should not requiring proprietary OS to functioning.
It's not the; there are plenty of others. And it doesn't require a proprietary OS to function. People run it on Wine and Mono on various other non windows OS
It was written by .NET developers, because that's what they're familiar with. That was their choice.
The code is there (and GPL licenced), so feel free to port to whatever OS you see fit. It is not a trivial task to rewrite it.
AWB works fine under Wine.
I have been using it under Wine for more than two years. I have made a number of AWB source code changes to better support use under Linux and Wine.
The only functionality that I'm aware of as not working is the database scanner, which typically fails with an "unable to access memory location" type error after a few minutes. Also I find AWB seems to freeze or report a memory issue every 1000 edits or so, whereas I believe under Windows there is no such stability issue. However, that does not prevent significant use, and at times AWB is stable over several days.
In general stability and behaviour under Wine has improved over time, so the team behind wine do seem to be improving the Wine releases over time, so in addition to having a working setup now, in the medium term the prospects for AWB under wine look very good to me.
Not really working.
AWB will load under mono with some source code changes. I have been able to log in and make some edits. However, the diff view does not work (there seems to be no working implementation of .NET web browser under mono), and a number of other secondary features such as "make list" are not working. It is overall not usable and only a very technically proficient user should look into it. When the next release of opensuse is out I will at some point investigate behaviour under the latest Mono version to see if there is any significant improvement. While the mono project have done some great work providing a native .NET library, the lack of a web browser option suggests to me there is no short term prospect of AWB being usable under mono, due to mono limitations.
I do all mine using native MonoDevelop and run Nunit under Wine, with Linux. So for development there is no call on Windows or any proprietary tools.
Prospect of porting
I think it could be hundreds of days of work to fully port AWB to a cross platform language with native support (e.g. Java), or an alternative (web based or similar). We use some features specific to the .NET language that have no direct equivalent that I'm aware of in other languages. So while I'd welcome a serious effort to do a port by others, I don't have the knowledge of a suitable target platform/language, nor do I wish to spend hundreds of days reimplementing what is already there and working. It must be remembered, we are all volunteers.
Overall I do feel comfortable that I have made the effort enhance Wine compatibility for AWB, and am "dogfooding" by doing 100% of my AWB edits under Wine.