I found some questions here on how to create a SaaS. This much is easy, but what I don't understand is what makes an application a PaaS and not a SaaS. What lines does an application cross before we can start calling it a PaaS (platform as a service) and not just a SaaS (software as a service)? It seems like a small difference but I can't pinpoint it.
I would welcome even examples of PaaS if you can point something about them that makes them a PaaS and not a SaaS. A common name in this area is salesforce but I don't know much about the service itself to understand from it why it's a PaaS.
Edit: I feel that from a programmer's perspective, it's the same job, or no? I think the only difference is the PaaS is for developers as end users and SaaS is for regular users as end users. Does that sum it up?