UPDATE: I've added screens of the editor--really impressive stuff.
The next piece of content for Portal 2 is something slightly unexpected: an in-game map editor.
Valve says the editor will allow users to create both single and co-op stages, and will be “easy to use,” which suggests an interface much simpler than what is usually used to build levels for games.
Players will also apparently be able to “view, play and vote on them [levels] with a simple click.”