API based systems

I’ve been doing some flash/flex projects built on custom made API’s from a CMS companies. I have also been doing some prototyping against various systems that got API’s.

I am looking for what options there is out there, I have a hard time googling the API terms, as i get to much irrelevant hits, so I wonder if you can help me get an overview.

Here some of them i know of:

Mediawiki (not finished)
Salesforce (expensive CRM stuff, has its own flextoolkit and stuff and has free developer accounts)