So what would you say is the most interesting and innovative project from the Apache foundation? The Apache HTTP web server? It is the cornerstone of the internet but innovative? Naah. Struts? Also important and widespread but hardly ground-breaking.

My pick (and my liebling) is CouchDB - a document-oriented database that can be queried and indexed in a MapReduce fashion using JavaScript. It does not support SQL (or any relational model for that matter) nor does it support transactions. And yes, it has a terrible performance on ad hoc queries. But it is very lightweight, scales very well, supports replication out of the box and can be accessed by a simple HTTP protocol with a clean and simple RESTFull API.

So CouchDB is definitely not an Oracle or an MySQL challenger. Neither does CouchDB compete directly with object databases nor with persistent object systems like Gemstone Smalltalk Object Server, since you still have to convert the documents to objects by hand and the other way around.

But CouchDB compensates for all those missing properties of relational (and also object) databases by offering other features, such as simplicity, flexibility, scaling, replication, easy accessibility from almost any language. Did I mention that it is also free? And all of those things are often more important in the web world, so CouchDB can make your web app tick like a well oiled clock.

While quite a few people (including the developers) see CouchDB as an almost complete web development stack (with maybe the addition of some js library like jQuery), I find it interesting as a component in other web stacks, primarily Seaside. Smalltalkers might find it interesting that (at least in theory) the CouchDB default query language JavaScript could be replaced by some other language, such as Smalltalk.