continue: https://sourceforge.net/tracker/?func=detail&aid=3392214&group_id=2331&atid=202331
It seems that I c an reopen it.
This binary package is made for windows, but my project is a platform for command line tools to work in a graphical user-friendly way, and at least it works fine on Windows and Linux, and it should also work fine on FreeBSD. However, I haven't made a binary package for Linux platform. Source archives are available for other platforms other than Win32. I haven't seen a mailing list for UPX, maybe we could discuss this on the mailing list.
The link has been modified to http://download-mirror.savannah.gnu.org/releases/cmdlauncher/bin-packages/win32/upx/upx-cmdlauncher-20110816.zip
UPX supports more platforms than you've mentioned. It nice that your tool is multi platform, but if you look at the UPX homepage, you can see that the download section has executables for example DOS/i386 and Atari TOS-MiNT/m68k. For an "official" UPX gui all the platforms should be supported. And yes, it sounds like an impossible task.