DynaMIPS and Dynagen. DynaMIPS is virtualised Ciswco hardware, Dynagen lets you use DynaMIPS as a hypervisor and run lots of Ciscos on your desktop. Then all one needs is IOS images.

Emacs+SLIME+SBCL. They are my toys. Funfunfun. It may end up with server and network monitoring software, one day.

I usually use either gnuplot or hand-written graphing code (for when gnuplot doesn't do what I want) to graph stuff. Mostly the hand-written graphing is related to above-alluded-to network/server monitoring software.