NAMBLA (which is dedicated to The Daily Show with Jon Stewart) modifies the appearance of the default action bars (and pet/stance/granted-ability bars) to make them a bit cleaner. Here's a summary of what it changes:

• Hides the borders on all of the individual buttons.
• Removes the career resource-based "glow" on buttons (AM high magic, Shaman mork/gork, Swordmaster balance, etc).
• Makes the "white-out" effect of buttons on cooldown half as strong, so it's not quite as opaque.
• Removes the pointless "s" on the end of button cooldown text.
• Resizes the cooldown text on buttons to be a bit larger (for readability) and modifies the font slightly.
• Modifies the binding font slightly.

Note that NAMBLA does not have any in-game configuration, but any or all of the above can be disabled by editing the Lua file; instructions on how to disable them are in NAMBLA.lua inside the addon's directory. By editing the file, you can also hide keybind text if you so desire (again, directions are in the file).

• Note - if you're wondering about the name of this addon, click the link in the first sentence of the description. It's parody.