[Jtsummers]

Scheme as well. Notably, these languages are (mostly) capable of letting developers add new models of computing or software design on top of the base language in a way that appears natural as a user.

If you want OO in Scheme, you can do it (and various models of OO at that). If you want a concurrent model, you can do it. If you want a relational programming model, you can have it.

Try doing the same with, for example, C. You can accomplish it, but you have to jump through hoops or rely on OS libraries or other things. And it will rarely, if ever, feel "natural" within the language.