Programs for a Sorcerer Supreme

Hello, /prog/.

I know the subject is vague, so let me explain:

I'm confident I know some programming languages very well, but I feel my knowledge is lacking when it comes to many others. So I'm looking for programs that can sharpen up my skills. Stuff that requires one to use most of a language's features. What would you suggest?

C - compilers. Device drivers?
C++ - game engines?
Scheme - an interpreter?
Common Lisp - ?
Haskell - ?
Java - ?
.NET - ?
Scala - ?
Python - ?
Ruby - ?

>>33
He implied he already knows how to program. He was asking which specific programs he should write for each specific language so he could ``sharpen up'' his skills. Please read his post again.