Useful/Interesting/Related links

Wargames

OverTheWire - offer a number of very good exploitation challenges (not your average boring stuff).

SmashTheStack - also offer varios challenges, better than the average.

HackThisSite - their realistic web missions are definitely worth checking out (from beginner to pretty complicated).

Virtualization

QEMU - full virtualization. Together with kqemu (kernel module) offer reasonable performance, no special CPU features requried.

KVM - full virtualization. Requires CPU support (/proc/cpuid - vmx for Intel, svm for AMD).

XEN - can do paravirtualization but also full virtualization with CPU support.

VMware - full virtualization. They have a decent GUI if you are into that kind of thing.

VirtualBox - full virtualization. Developed by SUN, haven't used yet.

Virtual PC - Microsoft's offering. Haven't used (don't plan to, either).

User mode linux - full virtualization. Run a new kernel as a user process.

There are also quite a few paravirtualization/jailing approaches: Virtuozzo, OpenVZ, lguest, freebsd jails.

Also related: VDE - virtual distributed ethernet. While in Linux, bridges+forwarding work just as well most of the time, VDE gives you some extra tools.

Misc

Coding Horror - On Working Remotely - Some structure to follow for effective (geo)distributed teamwork