Live support software is a popular term for online chat

Online chat

Online chat may refer to any kind of communication over the Internet, that offers an instantaneous transmission of text-based messages from sender to receiver, hence the delay for visual access to the sent message shall not hamper the flow of communications in any of the directions...

 applications designed specifically to provide online assistance to users of a website.

Technology

The software enables the administrator or webmaster of a website to receive and respond to text communication from multiple users of the website. It is commonly used as a way for webmasters/site owners to instantly engage their website visitors; done both in a reactive and proactive fashion. By using this type of software, webmasters often are anticipating:
a) increased interactivity and trust with the website visitor;
b) (if an E-commerce site) increased sales/conversions.

Among the applications below there are some that use JavaScript

JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....

, Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

 or Flash Player to run directly inside the browser.
These on-line applications differ from classic software mostly because Website visitors don't have to install anything on their PCs and they can communicate freely with website's online agents. There are also live support software that goes beyond basic text chat, and offer such advanced communication capabilities as true VoIP (Voice over IP), application sharing, remote view, real-time website traffic monitoring, and remote form filling.

Typically live support applications will open a window that connects the user to an agent. Some software allow the users to be queued, so that one member of staff can deal with a customer and then automatically move on to the next customer. The customer's position in the queue is sometimes displayed.

Some live support applications are written in low-level languages (e.g., C++) and distributed as compiled software that must be installed on a server. Others are written in languages such as PHP

PHP

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

 and can be modified as desired. MySQL

MySQL

MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...

and Microsoft SQL Server are common database engines used.