Apache is the most popular web server on the Internet with more than 70% of the web sites on the Internet using Apache. The Apache HTTP Server is a project of the Apache Software Foundation and the software is free. Originally designed for Unix servers, Apache has been ported to Windows and other network operating systems (NOS). The name "Apache" was derived from the word "patchy" that the Apache developers used to describe early versions of their software. Apache provides a full range of Web server features, including CGI, SSL, and virtual domains. Apache also supports plug-in modules for extensibility.

Apache HTTP Server is an open source HTTP web server for Unix-like systems (BSD, Linux, and UNIX systems), Microsoft Windows, Novell Netware and other platforms.

Apache Incubator is the stepping stone for projects hoping to become fully fledged Apache Software Foundation projects. Code donations from external organisations and existing external projects wishing to move to Apache will enter through the Incubator.

The Apache Project is a collaborative software development effort aimed at creating a robust, commercial-grade, featureful, and freely-available source code implementation of an HTTP (Web) server. The project is jointly managed by a group of volunteers worldwide.

Apache Tomcat, also called Tomcat, is a web container developed at the Apache Software Foundation. Tomcat implements the servlet and the JavaServer Pages (JSP) specifications from Sun Microsystems, providing an environment for Java code to run in cooperation with a web server. It adds tools for configuration and management but can also be configured by editing configuration files that are normally XML-formatted. Because Tomcat includes its own HTTP server internally, it is also considered a standalone web server.

Application Program Interface (API) documentation refers to documentate the Application programming interface (API) functions and operation details, so that other programmers can continue developing in the project, or develop other software that make use of the projects API, without having to study the code itself.

AppleScript is an object-oriented shell language and command-line interface for Macintosh, beginning with System 7 Pro.

AppleShare is the file server software developed by Apple Computer, Inc. for Mac OS users to share files among Macintosh computers on the same network.

Applet is a little application that can be a utility or other simple program. Applets are often written in Java language which are attached to HTML documents. An applet runs in the context of another progam, for example a web browser. The applet must run in a container, which is provided by a host program, or through a plugin, or a variety of other applications including mobile devices that support the applet programming model. Unlike a program, an applet cannot run independently. It provides display features often with interaction with human users, and is usually stateless and has restricted security privileges. An applet characteristically performs a very narrow function that has no independent use. Hence, it is an application -let (Applet).

Application in computer software refers to a complete and self-contained program that helps the user accomplish a specific task. Application programs should be distinguished from system programs such as operating systems, which control the computer and run those application programs.