CRM 2013 has a new process type called Action, that is meant to encapsulate complex business logic into a process that is triggered on non-CRUD mechanisms. Actions can be associated to a specific entity, but can also be defined as global. Actions can be triggered through the web service SDK and client SDK, but they cannot be triggered by other workflows or actions. This limits the value of actions because they cannot be implemented in the middle of other business processes defined in workflows.
Workflows and Actions should be able to call other actions, in the same way that workflows can call other workflows. With this new capability, Actions would become incredibly useful.