In the PHP world, probably the Doctrine ODM for MongoDB is the most successful. This followes to the opularity of Mongo, which is a transitional product between SQL and NoSQL, still based on some relational concepts like queries. [...] The case for an ODM over a plain Mongo connection object is easy to make: you will still be able to use objects with proper encapsulation (like private fields and associations) and behavior (many methods) instead of extracting just a JSON package from your database.

He briefly mentions that the PECL extension for Mongo needs to be installed prior to trying out any of the examples. His first example shows how to create a DocumentManager (similar to the normal EntityManager for those familiar with Doctrine). He also shows an integration with the ORM and shares some of the findings he's made when it comes to versioning the resources (hint: annotations are your friend).

Consider you have a set of data that is changing dynamically for each page request and you need to cache that data the fastest way possible. You can't cache dynamic and unpredictable data as a whole, can you? Hence, we would put each data entry into cache separately to be able to fetch it separately and dynamically. But this means bombing your cache infrastructure with with requests.

They break it up into a few different topics - caching text elements on the page, two-tiered caching (grouping cached items), incremental caching and cache versioning. They don't share an example of their code unfortunately, but they do mention something about a possible contribution to the Zend_Cache component of the Zend Framework.