It's interesting to see the growing trend in this direction for PHP.
I wrote one a little while back[1] that does even less than this :) The only goal being to provide a simple way to execute classes from the web or command line with a default autoloading implementation and a way to inject new ones[2]
Personally a lot of my current direction in PHP comes from watching what's happening the node.js community - I like the way that there are a lot of small-ish packages/modules that are pretty independent.
I've written a couple of packages for RocketSled already which you can see on my github page if you're interested.
[1] https://github.com/iaindooley/RocketSled
[2] There are some obvious improvements that could be made to the current implementation which always parses the package tree ie. caching