YUI Compressor can compress .js or .css files.
I downloaded YUI Compressor 2.4.2 from http://yuilibrary.com/downloads/#yuicompressor.
However, its provided command-line interface might be a problem, so here came the graphics interface version.
Executable: yuicompressor-2.4.2-GUI.jar (Some browser might modify the extension name to ".zip". To execute it, rename it back to ".jar")
Source File: src.zip (Can be imported using eclipse)