RDDB 是一个 Ruby 开发的面向文档的数据库系统，其灵感来自 CouchDB。它具有以下特性：

* Documents are simply collections of name/value pairs.  * Views can be defined with Ruby code, mapping from a document to any other data structure, such as a String, Array or Hash.  * A reduce block can be defined to reduce the initial mapped data from a view.  * Views can be materialized to improve query performance.  * Datastores are pluggable. Current implementations are RAM, partitioned files and Amazon S3.  * Viewstores are pluggable. Current implementations are RAM, file system and Amazon S3.  * Materialization stores are pluggable. Current implementations are RAM, file system and Amazon S3.  * Distributed materialization may work, but it's going to be rewritten.

示例代码：

  # First create an database object    database = Rddb::Database.new      # Put some documents into it    database << {:name => 'John', :income => 35000}    database << {:name => 'Bob', :income => 40000}    database << {:name => 'Jim', :income => 37000}      # Create a view that will return the names    database.create_view('names') do |document, args|      document.name    end      # The result of querying will return an array of names    assert_equal ['John','Bob','Jim'], database.query('names')

项目主页：http://www.open-open.com/lib/view/home/1331131173437