Outer Glow is a mod that allows you to see when a player is nearby with their Hat (outer layer) enabled. It's a very simple mod that's awesome for Minecraft SMPs!
If you are not on Feather or Lunar Client, click here.
This version does not shift over usernames by a pixel (when it does, it is incompatible with Feather & Lunar), so they may look a little strange in tab.
