Online Editor

Let's say you're away from your computer and all you've got is a web browser. You'd still like to run a piece of code (e.g. to check an answer on SO). What are your options?
Let's create a list of on-line interpreters of various programming languages. Here are some examples:

• Haskell: http://tryhaskell.org/
• Scala: http://www.simplyscala.com/
• Many languages: http://ideone.com/
• Many languages: http://codepad.org/