It's an external command for Homebrew. It provides short descriptions for many Homebrew packages, and I hope to eventually include all Homebrew packages. You can also search for packages by description.
If you already know the name of a package, and you want to see a bit about it, that's easy:
$ brew desc mutt
mutt: Mongrel of Mail User Agents (part Elm, Pine, Mush, mh, etc)
If you know the kind of thing you're interested in, but not the name of specific items, that's easy too:
$ brew desc -s key-value
redis: A persistent key-value database with built-in net interface
kumofs: A scalable and highly available distributed key-value store
cassandra: Highly scalable, eventually consistent, distributed key-value store
Both -s and --search are acceptable. Searches are always case insensitive. (Notice that as a Homebrew external command, you invoke the script as brew desc.)
Download and put the file brew-desc.rb anywhere in your $PATH, and make it executable. For example:
mv brew-desc.rb ~/bin
chmod +x ~/bin/brew-desc.rb
Leave the name as is; Homebrew knows how to find it.
I got these descriptions from the MacPorts ports tree. After that, I edited them slightly to make them briefer. There are still at least 500 or so Homebrew formulas without descriptions here, and no doubt these descriptions could be better in many cases.
Please fork, add descriptions (or edit the ones already here) and send a pull request. Thanks.