JAKE  Beware, I didn't test this fully, but its not a DROP app at all, and when i choose a folder of files in its default settings (changed nothing) it processed my files in to the abyss...

Files were gone...  
(Version 1.0a1)

MACBUDDY  Does seem to work, but not as a drop App. You have to open your file from 'File > AddFile...' menu item.

Also, it changes the resolution of images to 72 dpi (most 'reducers' do), although it seems to do a fair job using 'Relative' Width/Height if the numbers are the same (ie:50/50).

Oh, and work with copies, if you need to preserve originals for archiving.  
(Version 1.0a1)