You might have had requirements where you have to build a configurable email page for messaging purpose. People use several ways to accomplish  this requirement. Message Catalog, Custom page/component are couple of ways to get around this requirement.

Many might have used Generic Templates for this purpose. For those who haven't, you can try this tip.

Generic Templates are basically for the work flow purpose. You can find this under:

Set Up HCM > Common Definitions > Approvals > Generic Templates

You can extend this feature for your custom email functions.

WL_TEMPLATE_GEN is the underlying record for Generic Templates. When you create templates, you will use %numbers for tagging various parameters in workflow

Read Further:http://ps.mytechspeak.com/2013/09/custom-email-templates-tip.html