MongoDB has introduced a new aggregation framework in version 2.1 that makes it easier to perform complex analytics tasks without having to write custom JavaScript. This framework allows users to specify a chain of operations, called a "pipeline," to apply to their documents, making it similar to a pipe in a Unix shell. The framework includes operators such as $match, $project, $unwind, and $group, which enable filtering, data manipulation, and aggregation capabilities. These new features are available only by compiling from source and are not intended for production use until MongoDB 2.2 is released. The aggregation framework provides a declarative way to perform operations on documents, making it easier to manipulate sub-parts of documents easily. It also includes expression evaluation to return computed values for virtual fields, which can be used to create new virtual fields from computed values.