I do. I run a service called "HashCache" which caches resources by hash ( http://hashcache.rkeene.org/ ). I use this as a central cache for build scripts which download resources from the Internet, and the upstream/origin server may go away.

I wrote a version in Crystal (v0.10, I think) and Tcl to compare the two:

Crystal: https://chiselapp.com/user/rkeene/repository/hashcache/artif...

Tcl: https://chiselapp.com/user/rkeene/repository/hashcache/artif...

I'm specifically interested in production settings, not toy projects. Using something in production is much more interesting.

I am making a simple bloggy webapp with Crystal.