Facter

Facter is used by puppet to gather data about the systems puppet is managing. It's actually fairly mature and doesn't need to be changed very often.

I haven't done it, but it should be trivial to make it work with other systems that need something like this.

Reasonably easy to write plugins for, though you'll need to know a little ruby to do it. I've written a few that are probably mostly only useful for my site; fairly little overhead beyond figuring out how to write the code to gather the data you need.