It can be extended by every user. Hypatia Electronic Library is a directory of research workers in Computer Science and Pure Mathematics, and a library of their papers. The installation is quite easy these days, the software is very reliable, and here is a list of businesses using Linux as well as a set of business case studies. Linux is computing for everybody. S.E. , and a new distribution called Stampede .
Caldera seems to aim primarily at commercial customers.
Here is a good overview. The SANE project works on scanner support for Linux. SecurityPortal has useful information for securing your Linux system. The alternative is the Secure SHell ssh . Unfortunately, the original implementation of ssh is impeded by increasingly restrictive licenses.