[plt-scheme] Languages and Tools

So, a slightly off-topic question, but... there are people on this list 
who will have ideas and opinions about the question. If it's too far 
off, someone will say so.

Question:
If you were writing a compiler today, what tools would you use?

When I say "tools", this runs the gamut from languages to libraries to 
techniques (which isn't a tool, I know)... but a broader or more 
appropriate term doesn't come to mind.

The "why" of the question is, naturally, of interest.

My question isn't entirely hypothetical... nor am I about to embark on a 
new compiler project. However, colleagues of mine are, and I'm curious 
what people outside of my immediate sphere think about this question. It 
doesn't strike me as a simple one.

Thanks,
Matt