Third party applications are programs written to work within operating systems, but are written by individuals or companies other than the provider of the operating system. For example, Microsoft® systems come packed with several software applications. Of these, any program authored by Microsoft is a first party application. Any program authored by a different company or an individual is a third party application; the same being true for Apple™ and Linux™ systems. In this equation the second party is the user.
Third party applications can be standalone programs or they can be small plugins that add functionality to an existing parent program. The former category is endless. On a typical system, standalone third party applications include tens of dozens of programs. Web browsers like Opera, Safari® and Firefox®; and email clients like Thunderbird®, The Bat!, and Pegasus are some examples of popular standalone third party applications. Most anti-virus programs, firewalls, multimedia programs — virtually any program not written by Microsoft®, Apple®, or Linux, yet made to work on those systems — falls into this category.
In some cases, computer users of Windows® operating systems consider it more secure to use standalone third party applications for tasks such as email, newsgroups, Web browsing and Internet Relay Chat (IRC). Microsoft® applications have traditionally been the target of the vast majority of hackers, viruses, Trojans and other security threats. By using a third party application, one theoretically lessens the degree of potential vulnerability.
A different kind of third party application provides additional functionality to a primary program. These types of third party applications are referred to as plugins or add-ons. The existing parent program might itself be a third party application, or a first party application. Examples include encryption plugins for email applications, multimedia plugins for Web browsers to watch movies or see Flash content, or plugins that read certain types of files, such as the Adobe® Acrobat® plugin used for .pdf files.
Although plugins and add-ons are available for first party applications, the vast majority are written for open source software. Microsoft® and Apple® do not make the source code of their proprietary operating systems available to the public, limiting the ability of a third party to write a plugin or add-on. Most third party applications are also proprietary, keeping source code a company secret.
However, there are many third party applications that are open source and this category of software is growing. The Firefox® Web browser and Thunderbird® email client are just two examples of open source third party applications that are quite popular. In part this is due to the ever-growing catalog of handy add-ons and plugins that are freely available for these programs. Open source first party applications are rare, with Linux operating systems creating the exception.