A few days ago, I came across a WAD with really cool scripts but no source included. To my dismay, the listacs utility available on the ZDoom download page only supports the old Hexen ACS format.
So, I decided to write my own disassembler. It should support all three formats: Hexen, ZDoom (ACSE), and ZDoom compact (ACSe).
This version includes a rudimentary decompiler as well, although it currently generates spaghetti code.
You'll need Python version 2.5 or later to run it. If you don't want to do a full install of Python, I have a standalone version (using Py2Exe) available here; however, since it includes the Python runtime, it's big (1.72MB) and my bandwidth is limited. If anyone else wants to host it, be my guest.
EDIT: Fixed some bugs.
I probably should have tried to re-compile the output before I posted. Apparently, ACC recognizes 'goto' as a keyword, but not as a statement. Also fixed a bug causing certain script types not to be recognized.