Actions in CRM is very powerful process type which makes encapsulation of Business Logic run at server side and called from both Server side and Client side.
I recently develop managed solution which will list entire Action metadata, which will be helpful for the consumers of the Actions to know Action schema name and Input and Output parameter names
Installed this managed solution and go to configuration link, it will list real time Action metadata.
For more details go to my CodePlex project https://crmactionmetadata.codeplex.com/
My Encounter with Dynamics CRM 