Linux is structured and modular. Owing to its modular nature it is extensible. It can be extended using open source software (OSS) that supports Linux. There are a number of OSS technologies available that cover nearly every domain of Information Technology. These can be integrated to create a bigger solution that use available OSS as building blocks.
Recently I have joined a university where we have deployed their IT infrastructure following the OSS paradigm. You can read about some of the technologies we have deployed there on this link.