Apple - Hide Adium (or any other app's) icon in the dock
I achieved this with a simple Terminal command:
defaults write /Applications/Adium.app/Contents/Info.plist LSUIElement true
Per defaults(1), "Defaults allows users to read, write, and delete Mac OS X user defaults from a command-line shell." So this is actually doing the same thing as the other answers here, but without manually editing the plist file, which makes it much safer, not to mention easier (and scriptable).
Yes there is a way : Simply go go the App, right click and show package contents. Go into Application/Contents and open the info.plist with a simple text editor. Add these Lines under the dict key :
<key>LSUIElement</key>
<true/>
Yes, there is a difference. NSUIElement is an old key. Since Apple introduced Launchd services, they use the LSUIElement key. This is also working for Adium, I just tested it.
If It says it can't save the file, simply copy it out of the folder to you desktop, edit it, and move it back into the App.
Keep in Mind, that with the LSUI element, the App is working in the Background. It keeps the menu icon, but your app won't appear in the App-Switcher (CMD+Tab) nor in the Force-Quit Menu.
Here is a Screenshot on how I did it :
I've found a way that works for me.
Originally, the user chillin told me I could just add this to the Info.plist file in between the dict tags using TextEdit:
<key>LSUIElement</key>
<true/>
But all I saw was some gibberish (look below for screenshots).
But then I installed XCode and opened the Info.plist file in Property List Editor.
To open Info.plist, go to your HD (eg. Macintosh HD) and open the Applications folder - Macintosh HD > Applications > Right Click Adium > Open Package Contents > Contents > Right Click Info.plist and open with Property List Editor. This will open this:
Then, click Add Item at the top and name the key as LSUIElement and the value checkbox should be checked (ie. 1 or True).
LSUIElement:
Specifies whether the app is an agent app, that is, an app that should not appear in the Dock or Force Quit window.
Source
Note: When you click the value field, the key is automatically renamed to Application is agent (UIElement)
It should then look like this:
Then you can open up Adium and it will still be in the Menu Bar but no longer in the Dock!
This is the Info.plist file I saw after using Property List Editor (I've highlighted one of the parts that changed):
As I said before, the method that the user chillin said worked for a few people but this worked for me. This is what I saw when chillin answered this question:
... where as I should have seen something like this (image via hotdigitalnews):
