Welcome to the third and final part of the series in which we look at five alternative databases you can use with PHP apps you might not have heard of. [...] In this final part of the series, we're going to finish up by looking at two outstanding, yet markedly different, databases: eXist DB and Hypertable. So let's get started.

As in the other two parts of the series, they include a brief overview of what each database is and some sample code showing it in use (and what you'll need to install to use it).