Gravis, do you know what a functional language is? I ask this question in all seriousness, because you respond as if my example was just "yet another" language. A functional language is very different from programming in C or C++.
Scheme is a dialect of Lisp. Maybe you have heard of that. Scheme is not used much industrially, but that doesn't mean learning a new way to solve problems won't make you a better programmer.
You say that "Assembly language is the most powerful as far as capabilities." This may be true in regards to the machine the assembly is designed to run on, but assembly is not portable. Again, I honestly wonder if you realize there are CPU architectures other than i386 out there; "Assembly" is not a single programming language. There's x86 assembly, MIPS assembly, PPC assembly etc. In any event, anything coded in assembly becomes useless when you stop using that CPU, which is a serious drawback. I would argue that C is a more powerful language. If you're thoughtful, most code you write in C can be used anywhere, and with any decent optimizing compiler, any performance cost over using the machine's assembly language will be negligible.
Scheme is a language of mostly academic interest. I would not write an operating system in it; I would write an operating system in C. Or maybe
Brainfuck. Brainfuck gets you really far in the real world.