Like Ruby on Rails, Merb is an MVC framework. Unlike Rails, Merb is ORM-agnostic, JavaScript library agnostic, and template language agnostic, preferring plugins that add in support for a particular feature rather than trying to produce a monolithic library with everything in the core. In fact, this is a guiding principle of the project, which has led to third-party support for the ActiveRecord, DataMapper, and Sequel ORMs.

In addition, it means that the core code in Merb is kept simple and well organised. This has multiple benefits. It means it’s faster for one thing. It’s also easier to understand, maintain and extend.

Merb is already packed with good stuff; flexible routing, gem plugins, the provides API, part and mail controllers etc. To get a better idea check out the features.