grsecurity is a complete security system for Linux 2.4 and 2.6 that implements a detection/prevention/containment strategy. It prevents most forms of address space modification, confines programs via its Role-Based Access Control system, hardens syscalls, provides full-featured auditing, and implements many of the OpenBSD randomness features. It was written for performance, ease-of-use, and security. The RBAC system has an intelligent learning mode that can generate least privilege policies for the entire system with no configuration. All of grsecurity supports a feature that logs the IP of the attacker that causes an alert or audit.
TrinityOS is a step-by-step, example-driven HOWTO on building a very functional Linux box with strong security in mind. TrinityOS is well known for its strong packet firewall ruleset, Chrooted and Split DNS (v9 and v8), secured Sendmail (8.x), Linux PPTP, Serial consoles and Reverse TELNET, DHCPd, SSHd, UPSes, system performance tuning, the automated TrinityOS-Security implementation scripts, and much more.
Hardened Debian improves Debian GNU/Linux with high security and hardening features, hardened kernels and packages, DHKP, and other security related enhancements. It makes systems more difficult to compromise using common attacks such as race conditions, chroot jail escapes, and buffer overflows.
guard bash is a shell wrapper that will execute an authentication phase before any command is executed. It uses a secret (user owned) algorithm method, and has a per user customizable procedure. If you need to connect to your computer from outside of your safe environment, even if you use SSH, you are vulnerable to simple attacks like key sniffing or to more complex attacks against SSH. If you have more than just one authentication method, you can more safely log in your account from an insecure Internet host.
The modular syslog allows for an easy implementation of input and output modules. The modules that mantain compatibility with its precursor are included in the standard distribution along with four modules: om_peo (an implementation of PEO-1 and L-PEO, two algorithmic protocols for integrity checking), om_mysql and om_pgsql (modules that sends output to a mysql and postgresql database, respectively) and om_regex (a module that allows output redirection using regular expressions).