ALL google services ("apps script"; "apps script gadget") in sites.google; "hello world" with GAS

Unlike browser-based JavaScript, the scripts you write run directly on Google servers in order to provide direct access to the products they control. 

The Google Apps Script language is JavaScript. The Google Apps platform holds a bounty of features that let one bring robust applications without the need for any software or server configuration (GAS use google servers). 

Google Apps Script (GAS) can be developed using the Script Editor in Sites.

Apps Script can be embedded in a Sites page using an Apps Script gadget (each Apps Script gadget uses a pre-developed Apps Script).

Before you start,

1) you MUST understand the security model of GAS :

 the owner of a script is the user who created that script. Every script embedded in a Sites page executes under the identity of the owner of the script or could be shared to.

2) you MUST understand the IU services (UI user Interface):

http://code.google.com/googleapps/appsscript/service_ui.html

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tutorial guides (Hello):

http://code.google.com/googleapps/appsscript/articles/getting-started-with-sites.html

list : 

 Google Apps Script API documentation:

http://code.google.com/googleapps/appsscript/allservices.html

 script templates gallery

http://code.google.com/googleapps/appsscript/templates.html

GAS blog:

http://googleappsscript.blogspot.com/

Updates:

http://code.google.com/googleapps/appsscript/release_notes.html

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https://sites.google.com/site/scriptsexamples/

http://code.google.com/googleapps/appsscript/guide.html

You don't have to be a programmer to use Google Apps Script.
If you're not a JavaScript programmer, read the whole document, which contains detailed walk-throughs of many code snippets and short programs:http://code.google.com/googleapps/appsscript/guide.html
 You'll find learning Google Apps Script easier if you are familiar with Spreadsheet macros (excel) and formulas and with programming logic structures such as loops, conditional statements, and switch statements.

---------------------first ex-ample: "the hello world" application
This tutorial guides you through the steps of creating a hello world application using Google Sites and Google Apps Script. You implement this application by embedding a script in a Google Sites page.
http://code.google.com/googleapps/appsscript/articles/getting-started-with-sites.html

https://sites.google.com/site/javascript2blogger/gas/hello-1