Voom is framework wrapped in a Drupal module. Voom is implemented in a way that allows you to interfaces with core drupal functionality in a way that will be more natural to developers that are coming from Rails or Java SpringMVC.  

Drupal Sandbox: http://drupal.org/sandbox/mgiacomi/1131452

If you are looking to build an extension to drupal core, or looking to provide extra functionality on top of an existing module, then don't bother with Voom. If you want to do custom application development, something you would generally consider using CakePHP or Rails for, than Voom is what you are looking for.

Here are some of Voom's features:

MVC: Voom allows you to create applications inside of Drupal using the Model-View-Controller paradigm. This encourages one to develop in a way that provides a high degree of separation between your models, controllers, and views. For more details see Model–view–controller Unlike generic MVC frameworks Voom has many Controller and Model features that are Drupal specific. Allowing you to achieve a higher level of Drupal integration.

OOP: Voom allows you to code in drupal using OOP. Your application will end up being wrapped in a module that Voom will bootstrap.

Dependency Injection: Voom acts as a small DI engine for Controller, Services, and DAO's in your module. This allows you to write code that is cleaner and can be more easily unit tested.

Annotation Support: Voom allows you to use annotations to do add declaratively add functionality to your application. We currently support annotations for dependency injection, menu support, breadcrumbs, transactions, and security.

Global Transactions: Voom abstracts Drupal's transactional support by allowing you annotate methods as transactional. This allows you to create transactional boundaries in services that may span may DAO. If an exception is thrown by the annotated method, then the transaction is rolled back otherwise it is committed. Transactional methods are commit or rollback all databases together. So if an annotated services method makes calls to DAO's using two different database, than a exception will rollback changes to both databases.
* This is not XA or 2 phase commit.