RPTools.net

I have been tweaking MT for a few days now, understanding the source, ease of feature injection (Specifically JS macros), etc.

I've ran into one major problem so far: The UI .xml files are not easily understandable to my eyes, and I can't get WindowBuilder to edit them.

My question is: What did the OPs use for designing these UIs?

They used an old and now sadly no longer under development tool called Albeille. You can find it here: https://java.net/projects/abeille