Save a node from another site
The Services module will definitely help you with that


  A standardized solution of integrating external applications with Drupal. Service callbacks may be used with multiple interfaces like REST, XMLRPC, JSON, JSON-RPC, SOAP, AMF, etc. This allows a Drupal site to provide web services via multiple interfaces while using the same callback code.


It has CRUD operations for nodes, files, users and plenty more. There's a video presentation available that introduces it properly, and there are loads of code samples on the web to get you started.