Well, I can only share a little. It's a web app built around a large, temporal knowledge base, with a proprietary data analytics engine that we develop in-house. The engine generates metrics and alerts that give our users decision-making insights. Gads, this sounds like the worst shit-head MBA project ever, but there is a lot I'm leaving out.

In the process, it's also a major test bench for a number of development tools we're building. This is where Racket pays dividends: it has a lot of the simple web-dev stuff in a good-enough state to get you off the ground fast, but doesn't pin you down to any one thing, leaving you wide open to rip out and replace whatever you want. Don't like how the HTML templating engine works? If you're good at macros (and Racket's macros are relatively easy), it's a simple job to roll your own.

We've got a data comprehension system that has its own pseudo-byte code that treats SQL like a machine-language in need of a VM that gives us a lot of static checking of our queries. We have a migration system that can rebuild the schema and restore data as easy as compiling your application, with reversible data translations between schema versions (so that we often do. Setting up a new developer-machine/test-environment/culster-node/what-have-you is a snap). Some of this stuff would have been damn costly to not just build without Racket's macros, I shudder to think what the changes we've had to make along the way would have been like.

Racket lets us take DRY to the extreme. Almost nothing in this project has been difficult to change, or at least no more difficult than the initial effort to develop it, because there is almost never a reason to change the interface to anything, and if it does need changing, the human-readable-code level has so few interaction points it's trivial to change interfaces. Hell, even in the case where a lot of interface changes would be necessary, we could probably just write a Racket program to chop up the S-expressions for us.

The mathematics library is also very good, providing a lot of intuitive, high-performance primitives that fit our data crunching needs. And we're currently investigating using the Prolog-like Datalog language mode

And the performance is extremely good, especially if you're coming from the Python/PHP/Ruby world. I find it as expressive as Python (actually, translating Python programs is nearly 1-to-1) but with performance more like static C#. The optimizer is very good and there is a typed version of Racket that gets optimized even more. Yeah, you should use Racket even if you don't plan on learning macros, because it's as easy as Python and its a lot faster.

All along the way. Graphics primitives: standard library feature. Parallel code: super-simple, very solid, and built in. Linear algebra: very solid, very easy to use (almost as easy as basic primitives) and again, built in. Distributed package management: built-in, it's part of the regular import syntax. Racket-to-JavaScript translator: well, not quite built in yet, but the package manager might as well let you treat it as so. Cross-platform compatibility: haven't had a single issue getting people on Linux, OS X, and Windows up and running with development yet.

If you've ever tried getting Scala or Clojure or Ruby setup on your own, Racket blows them out of the water.

I'm not terrible certain the fundamental premise of the project is sound, but at the end of the year we're going to have something of value on our hands, whether it's the raw data of the knowledge base or the development tools. Racket doesn't just let us build proof-of-concepts fast, it lets us expand them into heavy-lifting mode pretty quick, too.