With all the developer extensions in recent time around SharePoint (Features, Solutions etc), I've found there seems to be a few little known and little used 'other' APIs within the SharePoint space.

We've got things like WebServices and the SharePoint Object Model (SPSite etc) that we use however, there's a couple of other APIs that could be useful also for the times when you're not running locally on the SharePoint machine - they generally center around HTTP and extending it.

Two (that come immediately to my mind) are:

1. WebDav - early versions of 'Web Folders' used this.

2. RPC (over HTTP) APIs - Front Page and SharePoint Designer still use these.
(InfoPath when submitting forms uses this to promote properties to a forms library)

A great example of this is SharePad for SharePoint on CodePlex

Merry Christmas,

Mick.