A public-domain Web server developed by a loosely-knit group of programmers. The first version of Apache, based on the NCSA httpd Web server, was developed in 1995. Because it was developed from existing NCSA code plus various patches, it was called a patchy server - hence the name Apache Server. As a result of its sophisticated features, excellent performance, and low price (it's free), Apache has became the world's most popular Web server. By some estimates, it is used to host more than 50% of all Web sites in the world. Core development of the Apache Web server is performed by a group of about 20 volunteer programmers, called the Apache Group. However, because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons. In many respects, development of Apache is similar to development of the Linux operating system.