exploit-exercises.com provides a variety of virtual machines, documentation and challenges that can be used to learn about a variety of computer security issues such as privilege escalation, vulnerability analysis, exploit development, debugging, reverse engineering, and general cyber security issues.
Nebula covers a variety of simple and intermediate challenges that cover Linux privilege escalation, common scripting language issues, and file system race conditions.
Nebula is an ideal place to get started for people new to Linux exploitation.
Protostar introduces basic memory corruption issues such as buffer overflows, format strings and heap exploitation under "old-style" Linux system that does not have any form of modern exploit mitigiation systems enabled.
Protostar is the next progression from Nebula.
Fusion continues the memory corruption, format strings and heap exploitation but this time focusing on more advanced scenarios and modern protection systems.
Fusion is the place to start if you are familiar with Linux exploitation and wish to learn more about exploitation prevention systems.
Main Sequence is the Capture The Flag event from Ruxcon 2011. It provides a variety of challenges such as penetration tool usage, binary analysis, basic cryptographic analysis, client side exploitation, password cracking and general website hacking.
To be announced