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 - ?

>>2
Because having compiler compiled by a compiler compiled by another compiler compiled by another compiler compiled by yet another compiler compile your compiler means you get the worst things about all of them added together. All the bugs from 6 different compilers are now creating problems with your compiler, all the optimization problems from the pipeline of different compilers are added together, all the attack vectors are combined and you end up with a huge surface of complete shit. Writing a compiler or anything important (read: a device driver, an embedded system etc) has to be done close to the metal.

As far as the initial post goes:

Common Lisp/Scheme - See SICP

Haskell - Anything highly mathematical. Perhaps a CSG raytracer?

Java - Large OO business application. Eclipse plugin perhaps. Make sure you use SWT, Swing, XML, JavaBeans, Hibernate, Reflection, Collections (Generics), JSP.

.NET - Not a programming language.

Scala - No

Python - Web Browser

Ruby - >>3