This is an excellent article about the different types of Public Cloud PaaS platforms out there. (I bet you thought there was only one type of PaaS didn’t you? ) This blog post classifies them as:
- Metadata PaaS
- Framework PaaS
- Instance PaaS
It uses many PaaS examples to show where they fit. For instance Metadata PaaS products are likened to Microsoft Access in the cloud. (Some of my own examples that would seem to fit this taxonomy are Microsoft’s LightSwitch forms over data tool that can generate an app that can be deployed either on-premise or into Windows Azure, and the LongJump/AT&T cloud PaaS.)
I won’t steal his thunder concerning the rest, but I do invite you to read his full blog post.