Keep your clock synchronized to the second. Secure Shell Protocol. Make sure your connections to other network hosts on the Internet are transmitted confidentially. Simply the mother of all typesetting software. All of my handouts for math courses are typeset in LaTeX, which can be then converted into Adobe PostScript or Adobe Acrobat .
Acrobat viewers are available for free.
On August 1999, I added an iMac to the office to perform routine PC-ish tasks. Check out the math quotes server at Furman University.