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 - ?

>>34

Who cares? When I make threads, I don't necessarily expect the responses to be related to the topic - as long as we're discussing something in a somewhat serious manner, I couldn't care less if my Brainfuck Fibs implementation thread turns into a discussion on FPGA tripcode crackers.

Just be thankful that your responses in the thread are very closely related to the topic at hand - don't throw a hissy fit just because people aren't taking every last item of the topic into consideration. Go take a look around at some other /prog/ threads and realize that it's a god damned miracle that you even got this many serious replies.