Vapid Labs
- Lists vulnerabilities, white papers and utilities.
- http://vapid.dhs.org/

John the Ripper password cracker
- A portable password cracker with built-in efficient implementations of multiple password hashing algorithms found on various Unix flavors. Additionally supports Kerberos AFS and Windows NT LanMan hashes, plus many more with contributed patches. Officially
- http://www.openwall.com/john/

Rscan
- Tool that lets a system administrator run complex or simple scanner scripts on any number of machines in a heterogeneous environment. Unmaintained since 1995.
- http://www.protomatter.com/rscan/

Exploit World
- Archive of exploits for many systems. Pages have not been updated since 1998 and are preserved only for posterity.
- http://www.insecure.org/sploits.html