I was looking for a skin editor and there wasn't much here, so I looked around and found this. It is apparently based on e2skinner (which I never used...) and was updated last year, which is much more recent than anything else I found.
https://github.com/iMaxxx/OpenSkin-Designer
I installed (well just extracted the zip) and just started playing with it. It loaded a few skins without error and seems functional, but I haven't done much with it.
Is there something better that people are using? I am not interested in starting some new skin from scratch, just making a few changes to some existing skins (for alien2.)