JavaScript, jQuery, AJAX and related tools for client-side scripting

JavaScript

JavaScript is the dominant client-side scripting language for adding interactivity to web pages.

JavaScript frameworks

JavaScript frameworks simplify JavaScript development, with functions for common tasks like:
Dynamically select, read and change HTML and CSS
Handle events (page loads, errors, mouse movement, clicks, key presses, menu changes, etc.)
Create transitions and animations
Load and display data from sources such as AJAX or JSON
jQuery is probably the most popular JavaScript framework.
jQuery tutorial with interactive examples
Yui Library - JavaScript and CSS framework
Google Web Toolkit - development framework

AJAX - Asynchronous JavaScript and XML

Use JavaScript to get data from a server without a complete page reload or delaying a page load

XML

A general language to store, send and receive hierarchically structured data

RSS Feeds

XML data containing news and other changing information; subscribe using feed reader or email

Google Maps API

Click Add a map to your website. Select one or many locations or additional/advanced options.

Example of a map with multiple locations
Example of a mashup (data + interactive map)