Someone shoots you some Java source code, you try to just open it up in IntelliJ, and then you realize that you need a freaking project. Instead, you open it up in Textmate and go from there.
Hence, the definition of an IDE:
If you have to create a project before you to open a file, you are using an IDE
Good tools can be very rich, but not enforce this. Emacs can act as the mother of all IDEs when it comes to functionality, but you can also right click and open a darn file. At this point, I would never build a programming tool that didn’t work in either mode.