is built on a large foundation of open source software, and runs many more open source titles easily. The Macintosh operating system is built on a large foundation of open source software, and runs many more open source titles easily.
For example, the printing system and the windows file sharing in OS X use the same open source technologies as Linux. The Safari web browser shares the same rendering system of the Konqueror browser popular on Linux.
An excellent resource to find open source software for Mac OS X is OpenSourceMac.org.